Diet, Physical Activity, and UV Protection Comprehensively Influenced Vitamin D Status: A Cross-Section Study of Chinese College Students

doi:10.21203/rs.3.rs-1144529/v1

Background: Vitamin D deficiency is a major public health problem in China while there are seldom reports about vitamin D nutrition status in Chinese college students. The purpose of this study is to explore the vitamin D status of the college freshmen who came from different provinces of China and to comprehensive analyze the effects of diet, physical activity, and UV protection on serum vitamin D levels.

Methods: Totally 1,667 freshmen who came from 26 provinces, autonomous districts or municipalities, were recruited into this study. An online questionnaire was used to collect the information including demographic status, diet habit, physical activity, and UV protection of the participants. Serum 25(OH)D₃ concentrations were measured using a liquid chromatograph mass spectrometer. Multivariate linear regression analyses were used to explore the comprehensive influence of diet, physical activity, and UV protection on serum 25(OH)D₃ levels.

Results: The average age of the subjects was18.55±0.90 years, with 23.0% male and 77.0% female. The mean serum 25(OH)D₃ was 18.06±6.34ng/mL and the proportion of vitamin D deficiency and insufficiency was 67.5% and 27.8%, respectively. Multivariate linear regression indicated that milk and yogurt intake≥200mL/d, calcium or vitamin D supplements and average time of outdoor activity ≥60 min/day were positively linked to higher serum vitamin D while sweets intake ≥10g/d and higher UV protection index were negatively influenced serum vitamin D after adjusted for age, gender, students’ original residence, latitudes and longitude.

Conclusions: Vitamin D deficiency is an important health problem in Chinese college students. Milk and yogurt intake and outdoor activity should be encouraged while sweets intake should be limited for preventing vitamin D deficiency. Public health policies should consider well-balanced guidelines on UV protection and vitamin D food fortification or supplementation.

Endocrinology & Metabolism

Nutrition & Dietetics

Serum 25(OH)D3

Vitamin D deficiency

UV protection

Dietary intake

Physical activity

Vitamin D is a kind of soluble vitamin, which not only plays an important role in skeletal health, but also has several other health benefits such as prevention of cancer and autoimmune diseases, reduction in risk of cardiovascular disease, metabolic syndrome (MetS), and prevention of infections[1–5]. Therefore, maintaining adequate vitamin D levels in the body can help prevent these skeletal and non-skeletal diseases.

However, vitamin D deficiency is still a major public health problem worldwide nowadays [6–8]. The prevalence of Vitamin D deficiency and insufficiency among US adults in 2001–2010 were 28·9% and 41·4%, respectively [9]. In China, a cross-sectional study included 14,302 participants aged from 18 years old to 65 years old from six major cities indicated that the prevalence of 25(OH)D₃ concentration <30 ng/mL reached up to 83% [10]. The results from the Chinese National Nutrition and Health Survey (CNNHS) 2010–2012 indicated the prevalence of vitamin D deficiency in children and adolescents aged 6-17 was 53.2% at the cut-off of 20 ng/mL [11]. There are seldom reports about vitamin D nutrition status in college students as they usually have good health conditions. Considering the non-skeletal health benefits of vitamin D and from the point of view of disease early prevention using nutrition strategy, it is necessary to clarify whether vitamin D deficiency is also a nutritional problem in young people and its influencing factors.

The main sources of vitamin D in the body are sunlight, diet and vitamin D supplements⁴. A review by Engelsen O indicated that on the global level, the main source of vitamin D was the sun [12]. Serrano MA reported that around noon in January it took more than two hours of solar exposure to obtain the recommended daily dose of vitamin D, whereas the rest of the year ranged between 7 min on July and 31min on October in a northern mid-latitude [13]. At moderate to high latitudes, diet became an increasingly important source of vitamin D due to decreased solar intensity and cold temperatures, which discouraged skin exposure [12]. The research of Dimakopoulos I indicated that major food sources of vitamin D were fish (46%), meat (15%) and cereals (12%), however, over 90% of the population in all age groups did not meet the Estimated Average Requirement (EAR) [14]. Some studies also indicated that increased serum vitamin D occurred with physical activity both indoors and outdoors[15]. Most of the studies focused on the separate effects of dietary intake, UV radiation exposure or physical activity on serum vitamin D levels. But there is not a unique and adequate source of vitamin D for human and vitamin D status is usually the result of a combination of these factors above. Therefore, considering the comprehensive effects of dietary intake, physical activity, and UV protection on vitamin D levels has more practical meaning.

The purpose of this study is to explore the vitamin D status of the college freshmen who came from different provinces of China and to comprehensive analyze the effects of diet, physical activity, and UV protection on serum vitamin D levels. We hypothesized that dietary intake, physical activity and UV protection had comprehensive effects on serum vitamin D levels. Multivariate linear regression analyses would be used to explore the comprehensive influence of diet, physical activity, and UV protection on serum 25(OH)D₃ levels. This is critical for us to provide the theoretical supporting for the comprehensive life-style prevention of vitamin D deficiency.

2.1 Participants

The study subjects were freshmen of Shanghai University of Medicine and Health Sciences, started the school at 2020 September. They came from twenty-six different provinces of China and aged from sixteen to twenty-six. A total of 3,385 students who had completed physical examination were recruited into our study. Of these, 1,925 students completed questionnaires on diet and lifestyle. After excluding 257 students who had extreme values for total energy intake (<500 or >4500 kcal/d) and 1 case with obvious logic error in data, 1,667 subjects were eventually included in our analysis. This study protocol was approved by the Ethics Committee of Shanghai University of Medicine and Health Sciences (approval number:2019-CSHS-SUMHS-05-230119197901252329). A written informed consent was provided by all subjects.

2.2 Questionnaire Survey

The freshmen were taken a physical examination by trained medical personnel after they reported to university. An online questionnaire was used to collect the demographic information and the lifestyle information about the diet, physical activity, and UV protection of the participants. The first part of the questionnaire was the demographic information, including age, gender, original residence, ethnicity etc. The second part of the questionnaire was a simple food-frequency questionnaire (FFQ) which was designed by Gao J and the reliability and validity were reasonable. A total of 21 food categories that were common consumed in China were included in our FFQ questionnaire. The pictures of the standard amount of food were presented when the participants answered questions online. The reliability coefficients of food intakes ranged from 0.56 to 0.87(P<0.01) and the correlation coefficients of food intakes between simple FFQ, FFQ146 which including 146 food items, and 3d 24h dietary records ranged from 0.31 to 0.72(P<0.01)[16]. The third part of the questionnaire was about the UV protection. Four questions including whether to use sun hat, whether to use sun umbrella, whether to wear sun-protective clothing and whether to use sunscreen were asked to assess the participants’ UV protection. Each question has 5 choices including almost no use, occasional use in summer, frequent use in summer, always use in summer and use in all seasons. The UV protection index was used to assess the degree of the participants’ UV protection, and for each of the four questions, ‘almost no use’ calculated as ‘1’ point, ‘occasional use in summer’ calculated as ‘2’ point, ‘frequent use in summer’ calculated as ‘3’ point, ‘always use in summer’ calculated as ‘4’ point, ‘use in all seasons’ calculated as ‘5’ point. The UV protection index was an integral calculated though the degree of the four UV protection methods. Therefore, the scores of the UV protection index ranged from 4 to 20, the higher the score, the better the sun protection. The fourth part of the questionnaire was about the physical activities including the frequency and duration of vigorous physical activities, moderate physical activities and walking every week, as well as the average duration of the outdoor activities during the daytime every day in the last 1 year.

2.3 Serum Vitamin D Determination

Fasting venous blood samples were collected and transported in ice boxes to Shanghai Yulong Clinical Diagnostics Ins for assessment of serum 25(OH)D₃ concentration. Serum 25(OH)D₃ concentration was measured using a high performance liquid chromatograph (Agilent 1100; Agilent Technologies Inc., Santa Clara, CA, USA) and a mass spectrometer (API4000Q trap; AB SCIEX LLC., Redwood City, CA, USA). The lower limits of 25(OH)D₃ for detection was both 1.6 ng/mL. The test sensitivity was assessed with the inter-batch coefficient of variation (CV) of 5.85% and between batches CV of 6.18%.

According to the recommendation of Chinese Medical Association based on the Consensus of the Chinese Society of Osteoporosis and Bone Mineral Research, circulating 25(OH)D₃< 10 ng/mL was considered severely deficient, 10~<20 ng/mL deficient, 20~<30 ng/mL insufficient, and ≥ 30 ng/mL sufficient[17].

2.4 Statistical Analyses

SPSS 22.0 was used for statistical analysis. Serum 25(OH)D₃ concentrations were expressed as P₅₀ (P₂₅–P₇₅) because they were not consistent with the normal distribution according to the normality test, and then they were compared by nonparametric test. The category variables were expressed as frequency (percentage). Multiple linear regression analysis was used to screen the dietary factors that influence serum 25(OH)D₃ levels. Since the distribution of serum 25(OH)D₃ levels was slightly skewed, we used the log-transformed serum 25(OH)D₃ levels as a dependent variable, the independent variables including 21 food groups, and at the same time age, gender and total energy intake was adjusted in the model.

Finally, multiple linear regression analysis was used to consider the comprehensive effects of diet, physical activity, and UV protection on serum 25(OH)D₃ levels, including the log-transformed serum 25(OH)D₃ levels as dependent variable and the variables which had statistical significance (P<0.05) in the univariate analysis and in dietary factors screening as the independent variable, adjusted with age, gender, student’s original residence, taken calcium or vitamin D supplements, latitudes (as continuous variables) and longitude (as continuous variables). A two-sided P < 0.05 was considered statistically significant.

3.1 Basic characteristics of the participants

A total of 1,667 participants with complete data were included in this study, including 383 males (23.0%) and 1,284 females (77.0%). The participants came from twenty-six provinces, autonomous districts or municipalities of China with an age ranged from 17 to 26 years old, and the average age was 18.55±0.90 years. Levels of serum 25(OH)D₃ of the participants ranged from 5.20 ng/mL to 64.83 ng/mL with the mean of 18.06±6.34ng/mL. The proportion of vitamin D deficiency (<20 ng/mL) and insufficiency (20~ <30 ng/mL) was 67.5% and 27.8%, respectively, and 4.4% of them were severe deficiency (<10 ng/mL).

Basic characteristics with the serum 25(OH)D₃ levels of the participants were shown in Table (1). The serum 25(OH)D₃ levels of male was higher than female, and participants who came from countryside and town had higher serum 25(OH)D₃ levels than those came from city. And participants came from central longitude had relatively higher serum 25(OH)D₃ levels.

3.2 Serum 25(OH)D₃levels of the participants in different food intake amount groups for 21 food items

To compare the difference of serum 25(OH)D₃ levels in different food intake amount, each food item from the simple FFQ was divided into two groups according to the common amount intake: high intake group and low intake group. The serum 25(OH)D₃ levels in different food items groups were shown in Table (2). Participants in high intake groups of refined rice, whole grains, milk and yogurt, eggs or river shrimp and crab had higher serum 25(OH)D₃ levels than those in low intake groups. Participants who took sweets ≥10g/d had lower serum 25(OH)D₃ levels than those took sweets <10g/d. And participants who had taken calcium or vitamin D supplements within 3 months had higher serum 25(OH)D₃ levels than those without supplements.

3.3 Multivariate linear regression analysis on screening dietary factors affecting serum 25(OH)D ₃ levels

Multivariate linear regression analysis indicated that milk and yogurt intake was significantly associated with higher serum 25(OH)D₃ levels and sweets intake was reversely associated with serum 25(OH)D3 levels as shown in Table (3).

3.4 Serum 25(Oh)d Levels In Different Uv Protection Categories

Serum 25(OH)D₃ levels in different UV protection methods were shown in Fig. (1A). Participants with different UV protection degree had different serum 25(OH)D₃ levels no matter which type of UV protection methods was used. Participants with good UV protection tended to have low serum 25(OH)D₃ levels (P<0.05).

In terms of UV protection index, the higher the UV protection index, the better the UV protection. It was indicated that serum 25(OH)D₃ levels decreased with the increase of the UV protection index as shown in Fig. (1B).

3.5 Serum 25(OH)D ₃ levels in different physical activity and BMI categories

Serum 25(OH)D₃ levels in physical activity and BMI categories were shown in Table (4). Participants who had outdoor activity time ≥60 min/day had higher serum 25(OH)D₃ levels than others and participants whose BMI <18.5 had lower serum 25(OH)D₃ levels than others.

3.6 Effects of diet, physical activity and UV protection on serum 25(OH)D ₃ levels

When variables of diet, physical activity and UV protection were put in one multivariate linear regression analysis model, results showed that milk and yogurt intake≥200mL/d, taken calcium or vitamin D supplements and average time of outdoor activity ≥60 min/day were significantly associated with higher serum 25(OH)D₃ levels and sweets intake ≥10g/d, was significantly associated with lower serum 25(OH)D₃ levels, after adjusted for age, gender, students’ original residence, latitudes and longitude, while UV protection index was inversely associated with serum 25(OH)D₃ levels (P<0.05) as shown in Table (5).There was no interaction among the variables of diet intake, average time of outdoor activity per day and UV protection index (data not shown).

In this study, we tested the vitamin D status in 1,667 college freshmen who came from 26 different provinces of China and explored the association of diet, physical activity, and UV protection with Vitamin D status in China for the first time. The mean serum 25(OH)D₃ levels were 18.06ng/ml and the prevalence of vitamin D deficiency (<20 ng/mL) and insufficiency (20~ <30 ng/mL) was 67.5% and 27.8% respectively. When factors of diet, physical activity, UV protection and calcium or vitamin D supplementation were considered in one multivariate linear regression analysis model, milk and yogurt intake, sweets intake, calcium or vitamin D supplementation, outdoor activity time and UV protection were independent influencing factors of vitamin D levels in college students. Milk and yogurt intake, calcium and vitamin D supplementation were positively linked to higher serum vitamin D, while sweet and UV protection were negatively influenced serum vitamin D. Therefore, dietary intake, physical activity and UV protection had comprehensive effects on serum vitamin D levels.

Studies have shown that vitamin D deficiency is still widespread around the world [7, 8]. But most of the studies focused on adults, children, pregnant or lactating women [9, 18–20]. The study about the vitamin D status in college students was very limited. Nimri LF reported vitamin D deficiency reached 47.92%, and the mean 25(OH)D₃ levels were 21.67ng/mL among US female college students. The mean serum 25(OH)D₃ level was 18.06 ng/ml in our study, and the mean serum 25(OH)D₃ level was 17.15 ng/ml in female which was much lower than the US college students[21], and also lower than that in the elderly Chinese population (24.4ng/ml)[22]. Our results indicated that vitamin D deficiency and insufficiency were serious in Chinese college students. Since vitamin D was influenced by ethnicity, geographical location, season, outdoor activity, diet and UV protection, our study focused on modifiable factors such as outdoor activity, diet and UV protection to explore the feasibility of preventing vitamin D deficiency from a lifestyle perspective.

Vitamin D is synthesized in the skin but can also be obtained from foods and supplements. Some studies had shown that milk consumers consistently had higher serum vitamin D levels [23, 24]. The results of the US National Health and Nutrition Examination Survey (NHANES 2001–2010) demonstrated a significant association between milk consumption and serum vitamin D status in US population, and the probability of meeting vitamin D recommendations was greater in milk consumers vs. non-consumers [23]. The reason may be that almost all milk in the US was fortified with 100 IU/cup vitamin D irrespective of the type of milk. Whereas in China, not all milk was fortified with vitamin D, we still found that milk and yogurt intake≥200mL/d was significantly associated with higher serum 25(OH)D₃ levels in college students. The Dietary Guidelines for Chinese Residents (2016) recommended a variety of dairy products, equivalent to 300 g of liquid milk per day [25]. However, in our study, only 25% of the participants met the recommendation for milk. Therefore, encouraging milk intake may be an effective strategy to improve the vitamin D status for Chinese college students. And the effect of milk on vitamin D levels still needs to be confirmed by further prospective studies, in order to provide more powerful evidence for nutritional prevention strategies for vitamin D deficiency.

Another dietary factor which had independent influence on serum 25(OH)D₃ levels was sweets intake in our study. The sweets intake ≥10g/d group was significantly associated with lower serum 25(OH)D₃ levels in Chinese college students. A monitored data from Korea National Health and Nutrition Examination Survey (KNHANES) had shown there had been increasing trends in children, and teenagers who consume sugary drinks and at the same time a significant trend toward lower serum 25(OH)D levels and a significant increase in the prevalence of vitamin D deficiency[26]. So far the study about the relationship between sweets or sugar intake and serum vitamin D status is limited. But the current evidence suggested an association of sweets or sugar intake with vitamin D status, which needs to be further clarified in details.

Since very few foods naturally contain vitamin D, the intake of vitamin D from foods is very low worldwide and well below the EAR [14, 27]. Therefore, vitamin D supplementation sometimes is considered a strategy to improve vitamin D deficiency. Numerous agencies and scientific organizations reached a consensus that serum 25(OH)D₃ concentrations of 30-50 ng/mL (75-125 nmol/L) are beneficial for overall health and in the absence of regular sun exposure, using appropriate doses of vitamin D supplements are the most efficient way to improve serum vitamin D status[28]. However, the current vitamin D supplement guidelines in China only apply to infants, women in late pregnancy or the prevention of osteoporosis [29, 30], and there is no guideline on vitamin D supplement for “healthy” young people in China. American association of clinical endocrinologist medical guidelines suggested that low bone mass and skeletal fragility in adults may be the result of low peak bone mass in early adulthood, excessive bone loss in later life, or both[31]. Whereas peak adult bone mass is usually attained in the late teens or early 20s[32]. Vitamin D is also associated with non-skeletal diseases, including cardiovascular disease, metabolic syndrome (MetS) and cancer [1–3]. And health conditions in early life including childhood and youth, would influence risks of disease in middle and old age [33]. These collectively suggest that maintaining adequate vitamin D levels in early adulthood can help prevent these skeletal and non-skeletal diseases later in life, and it is important for us to clarify the nutritional status of vitamin D in college students. In our study, only 4.7% participants met the recommendation of serum 25(OH)D₃ concentrations 30-50 ng/mL, and only 7.9% participants took calcium or vitamin D supplements, and participants who took calcium or vitamin D supplements had higher serum 25(OH)D₃ levels in our study. We think it is necessary to consider formulating corresponding vitamin D supplementation programs for Chinese college students, in condition of the sun exposure and dietary intake is not enough.

On the global level, the main source of vitamin D is the sun[12]. However, UV radiation is a double-edged sword, excessive UV exposure leads to non-melanoma skin cancer while lack of UV exposure leads to vitamin D deficiency[34]. More and more people take measures against UV exposure nowadays[35]. In this study, we used the UV protection index to assess the comprehensive degree of the participants’ UV protection. The range of the UV protection index was from 4 to 20 and the median of the UV protection index of our participants was 8 in our study, with male 4 and female 9 (P<0.001). Participants with higher UV protection index tended to have low serum 25(OH)D₃ levels and serum 25(OH)D₃ levels decreased with the increase of the UV protection index. Since the college students especially female at this age in China usually pay more attention to UV protection, it is necessary to develop a well-balanced guideline on UV protection that ensure an adequate vitamin D status and also skin protection.

The relationship between physical activity and serum vitamin D has also been concerned by some researchers. The findings of the analysis based on data from the US NHANES indicated that physical activity was associated with high serum levels of vitamin D regardless of indoor or outdoor practice, but the association was stronger in outdoor compared with indoor environments [15, 36]. In this study, total hours of physical activity per week was not an independent factor for serum 25(OH)D₃ levels, whereas average time of outdoor activity ≥60 min/day was significantly associated with higher serum 25(OH)D₃ levels. Therefore, the relationship between outdoor activity and serum 25(OH)D₃ levels is still attributed to the UV exposure of Chinese college students. The controversy about the relationship between physical activity and serum vitamin D status needs to be clarified in further extensive research. However, spending more than one hour a day for outdoor activity should be encouraged for the aim of increasing serum 25(OH)D₃ levels in Chinese college students according to our study.

The strength of our study was that the participants of our study came from 26 different provinces which covered a wide geographical range of China, therefore, the sample was well representative. Taking college students as research subjects, we comprehensively compared the association of diet, physical activity, and UV protection with Vitamin D status, thus filling the research blank of vitamin D deficiency in related fields of China. There were still some limitations in our study. First, the information of diet, physical activity, and UV protection were got from the online questionnaire filled out by students themselves which may lead to selection bias, although we had provided filling explanation before investigation. Second, the result came from the cross-section study, although we adjusted the common confounding factors in the multivariate linear regression, unknown confounding factors are still hard to avoid. The causal association of diet, physical activity and UV protection with vitamin D status needs to be clarified by further prospective studies.

Chinese college students have relatively low levels of vitamin D, and vitamin D deficiency is an important health problem. Milk and yogurt intake and outdoor activity should be encouraged, while sweets intake should be limited in Chinese college students for the aim of preventing vitamin D deficiency. Public health policies should make a well-balanced guideline on UV protection. At the same time, whether vitamin D food fortification or vitamin D supplements could be considered to ensure an adequate vitamin D status in Chinese college students should be further discussed.

CNNHS

Chinese National Nutrition and Health Survey

CV

coefficient of variation

EAR

Estimated Average Requirement

FFQ

food-frequency questionnaire

KNHANES

Korea National Health and Nutrition Examination Survey

MetS

Metabolic syndrome

NHANES

National Health and Nutrition Examination Survey

Ethics approval and consent to participate

This study protocol was approved by the Ethics Committee of Shanghai University of Medicine and Health Sciences (approval number:2019-CSHS-SUMHS-05-230119197901252329). A written informed consent was provided by all subjects.

Consent for publication

All authors consented for publication.

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request..

Competing interests

The authors declare that they have no conflicts of interest.

Funding

Project supported by the National Natural Science Foundation of China (Grant NO.81872614)

Authors' contributions

Lixin Na: Conception and design of the work, substantively revised the work

Yingyi Luo: Data curation, Investigation, drafted the work.

Chunbo Qu: Supervision, Project administration.

Rui Zhang: Data curation, Investigation.

Jingyi Zhang: Data curation, Investigation.

Dan Han: Data curation, Investigation.

Qingwen Zhang: Data curation, Investigation.

Jiaxing Li: Data curation, Investigation.

All authors critically reviewed the manuscript and approved the final version submitted for publication.

Acknowledgements

Not applicable.

[1] Wang T, Sun H, Ge H, Liu X, Yu F, Han H, et al. Association between vitamin D and risk of cardiovascular disease in Chinese rural population. PLoS One 2019; 14: e0217311. doi: 10.1371/journal.pone.0217311.

[2] Zhang R, Li B, Gao X, Tian R, Pan Y, Jiang Y, et al. Serum 25-hydroxyvitamin D and the risk of cardiovascular disease: dose-response meta-analysis of prospective studies. Am J Clin Nutr 2017; 105: 810-9. doi: 10.3945/ajcn.116.140392.

[3] Liu L, Cao Z, Lu F, Liu Y, Lv Y, Qu Y, et al. Vitamin D deficiency and metabolic syndrome in elderly Chinese individuals: evidence from CLHLS. Nutr Metab (Lond) 2020; 17: 58. doi: 10.1186/s12986-020-00479-3.

[4] Wacker M, Holick MF. Vitamin D - effects on skeletal and extraskeletal health and the need for supplementation. Nutrients 2013; 5: 111-48. doi: 10.3390/nu5010111.

[5] Feldman D, Krishnan AV, Swami S, Giovannucci E, Feldman BJ. The role of vitamin D in reducing cancer risk and progression. Nat Rev Cancer 2014; 14: 342-57. doi: 10.1038/nrc3691.

[6] Cashman KD, Dowling KG, Skrabakova Z, Gonzalez-Gross M, Valtueña J, De Henauw S, et al. Vitamin D deficiency in Europe: pandemic? Am J Clin Nutr 2016; 103: 1033-44. doi: 10.3945/ajcn.115.120873.

[7] Palacios C, Gonzalez L. Is vitamin D deficiency a major global public health problem? J Steroid Biochem Mol Biol 2014; 144 Pt A: 138-45. doi: 10.1016/j.jsbmb.2013.11.003.

[8] Van Schoor N, Lips P. Global Overview of Vitamin D Status. Endocrinol Metab Clin North Am 2017; 46: 845-70. doi: 10.1016/j.ecl.2017.07.002.

[9] Liu X, Baylin A, Levy PD. Vitamin D deficiency and insufficiency among US adults: prevalence, predictors and clinical implications. Br J Nutr 2018; 119: 928-36. doi: 10.1017/S0007114518000491.

[10] Jiang W, Wu DB, Xiao GB, Ding B, Chen EQ. An epidemiology survey of vitamin D deficiency and its influencing factors. Med Clin (Barc) 2020; 154: 7-12. doi: 10.1016/j.medcli.2019.03.019.

[11] Hu Y, Chen J, Wang R, Li M, Yun C, Li W, et al. Vitamin D Nutritional Status and its Related Factors for Chinese Children and Adolescents in 2010-2012. Nutrients 2017; 9:1024. doi: 10.3390/nu9091024.

[12] Engelsen O. The relationship between ultraviolet radiation exposure and vitamin D status. Nutrients 2010; 2: 482-95. doi: 10.3390/nu2050482.

[13] Serrano MA, Canada J, Moreno JC, Gurrea G. Solar ultraviolet doses and vitamin D in a northern mid-latitude. Sci Total Environ 2017; 574: 744-50. doi: 10.1016/j.scitotenv.2016.09.102.

[14] Dimakopoulos I, Magriplis E, Mitsopoulou AV, Karageorgou D, Bakogianni I, Micha R, et al. Intake and contribution of food groups to vitamin D intake in a representative sample of adult Greek population. Nutrition 2020; 72: 110641. doi: 10.1016/j.nut.2019.110641.

[15] Fernandes MR, Barreto WDRJ. Association between physical activity and vitamin D: A narrative literature review. Rev Assoc Med Bras (1992) 2017; 63: 550-6. doi: 10.1590/1806-9282.63.06.550.

[16] Gao. J, Fei. J, Jiang. L, et.al. Assessment of the reproducibility and validity of a simple food -frequency questionnaire used in dietary patterns studies. Acta Nutrimenta Sinica 2011; 33: 452-6.

[17] Xia. W, Zhang. Z, Lin. H. Consensus recommendations on vitamin D and their analogs (Chinese). Chin J Osteoporos Bone Miner Res 2018; 11: 1-19.

[18] Zhao Y, Yu Y, Li H, Chang Z, Li Y, Duan Y, et al. Vitamin D status and the prevalence of deficiency in lactating women from eight provinces and municipalities in China. PLoS One 2017; 12: e0174378. doi: 10.1371/journal.pone.0174378.

[19] Yang C, Mao M, Ping L, Yu D. Prevalence of vitamin D deficiency and insufficiency among 460,537 children in 825 hospitals from 18 provinces in mainland China. Medicine (Baltimore) 2020; 99: e22463. doi: 10.1097/MD.0000000000022463.

[20] Kanatani KT, Nakayama T, Adachi Y, Hamazaki K, Onishi K, Konishi Y, et al. High frequency of vitamin D deficiency in current pregnant Japanese women associated with UV avoidance and hypo-vitamin D diet. PLoS One 2019; 14: e0213264. doi: 10.1371/journal.pone.0213264.

[21] Nimri LF. Vitamin D status of female UAE college students and associated risk factors. J Public Health (Oxf) 2018; 40: e284-e90. doi: 10.1093/pubmed/fdy009.

[22] Chen J, Yun C, He Y, Piao J, Yang L, Yang X. Vitamin D status among the elderly Chinese population: a cross-sectional analysis of the 2010-2013 China national nutrition and health survey (CNNHS). Nutr J 2017; 16: 3. doi: 10.1186/s12937-016-0224-3.

[23] Torres-Gonzalez M, Cifelli CJ, Agarwal S, Fulgoni VL, 3rd. Association of Milk Consumption and Vitamin D Status in the US Population by Ethnicity: NHANES 2001-2010 Analysis. Nutrients 2020; 12:3720. doi: 10.3390/nu12123720.

[24] Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res 2011; 31: 48-54. doi: 10.1016/j.nutres.2010.12.001.

[25] Wang SS, Lay S, Yu HN, Shen SR. Dietary Guidelines for Chinese Residents (2016): comments and comparisons. J Zhejiang Univ Sci B 2016; 17: 649-56. doi: 10.1631/jzus.B1600341.

[26] Kang M, Choi SY, Jung M. Dietary intake and nutritional status of Korean children and adolescents: a review of national survey data. Clin Exp Pediatr 2021; 64: 443-58. doi: 10.3345/cep.2020.01655.

[27] Spiro A, Buttriss JL. Vitamin D: An overview of vitamin D status and intake in Europe. Nutr Bull 2014; 39: 322-50. doi: 10.1111/nbu.12108.

[28] Pludowski P, Holick MF, Grant WB, Konstantynowicz J, Mascarenhas MR, Haq A, et al. Vitamin D supplementation guidelines. J Steroid Biochem Mol Biol 2018; 175: 125-35. doi: 10.1016/j.jsbmb.2017.01.021.

[29] Zhou. J, Liu. Z. The progress in global clinical guidelines on the prevention and treatment of osteoporosis using calcium and vitamin D supplementation. Chin J Osteoporos 2017; 23: 371-80.

[30] Yang. S, Wu. G. Vitamin D deficiency and lack of vitamin D rachitis prevention advice. Chinese journal of child care 2015; 23: 680-3.

[31] Watts NB, Bilezikian JP, Camacho PM, Greenspan SL, Harris ST, Hodgson SF, et al. American Association Of Clinical Endocrinologists Medical Guidelines For Clinical Practice For The Diagnosis And Treatment Of Postmenopausal Osteoporosis: Executive Summary Of Recommendations. Endocr Pract 2010; 16: 1016-9. doi: 10.4158/ep.16.6.1016.

[32] Lin YC, Lyle RM, Weaver CM, McCabe LD, McCabe GP, Johnston CC, et al. Peak spine and femoral neck bone mass in young women. Bone 2003; 32: 546-53. doi: 10.1016/s8756-3282(03)00062-0.

[33] Hoffman DJ, Reynolds RM, Hardy DB. Developmental origins of health and disease: current knowledge and potential mechanisms. Nutr Rev 2017; 75: 951-70. doi: 10.1093/nutrit/nux053.

[34] Reichrath J. Skin cancer prevention and UV-protection: how to avoid vitamin D-deficiency? Br J Dermatol 2009; 161 Suppl 3: 54-60. doi: 10.1111/j.1365-2133.2009.09450.x.

[35] Miljkovic SV, Ljeskovic NJ. Sun protection behavior among adolescents - a comparative study conducted in 2008 and 2012. Med Pregl 2016; 69: 281-7. doi: 10.2298/mpns1610281m.

[36] Scragg R, Camargo CA, Jr. Frequency of leisure-time physical activity and serum 25-hydroxyvitamin D levels in the US population: results from the Third National Health and Nutrition Examination Survey. Am J Epidemiol 2008; 168: 577-86; discussion 87-91. doi: 10.1093/aje/kwn163.

Table1 Characteristics of the participants with serum 25(OH)D₃ levels (n=1,667)

Variables	n%	25(OH)D₃(ng/mL) ¹	P value ²
Age
16-17	31(1.9)	18.00(15.70-20.05)	0.317
18-19	1492(89.5)	17.00(13.50-21.40)
20-26	144(8.6)	17.51(14.27-22.42)
Gender
Male	383(23.0)	20.40(15.85-25.53)	<0.001
Female	1284(77.0)	16.16(13.01-20.25)	<0.001
Region of original residence
City	1072(64.3)	16.20(13.05-20.69)	<0.001
Town	197(11.8)	18.70(14.30-22.89)
Countryside	398(23.9)	18.40(14.66-22.67)
Ethnicity
The Han Ethnic	1591(95.4)	17.07(13.51-21.50)	0.697
The Minorities	76(4.6)	16.70(13.61-19.93)	0.697
Taken calcium or vitamin D supplements within 3 months
Yes	132(7.9)	18.81(15.19-23.31)	0.005
No	1535(92.1)	16.96(13.50-21.36)	0.005
Latitude
18°N ~24°N	37(2.2)	19.28(14.23-26.33)	0.069
25°N ~34°N	1437(86.2)	16.97(13.40-21.31)
35°N ~44°N	176(10.6)	18.21(14.39-21.77)
45°N ~49°N	17(1.0)	17.59(13.45-24.19)
Longitude
76°E~94°E	36(2.2)	15.62(12.85-18.73)	<0.001
95°E~114°E	241(14.5)	19.00(15.21-23.12)
115°E~131°E	1390(83.4)	16.81(13.30-21.16)

¹ Serum 25(OH)D3 levels were expressed as P₅₀ (P₂₅–P₇₅)

² P value for the nonparametric test

Table2 Serum 25(OH)D₃ levels of the participants in different food intake amount groups for 21 food items (n=1,667)

Food items	N（%）	25(OH)D₃(ng/mL)	P value
Refined rice, steamed
<200g /d	568(34.1)	16.30（13.01-20.81）	0.006
≥200g /d	1099(65.9)	17.32（13.79-21.68）	0.006
Refined rice, porridge
<50g /d	1010(60.6)	16.97（13.51-21.40）	0.236
≥50g /d	657(39.4)	17.30（13.57-21.50）	0.236
Refined wheat products
<50g /d	707(42.4)	17.10（13.43-21.30）	0.575
≥50g /d	960(57.6)	17.02（13.60-21.59）	0.575
Desserts
<25g /d	926(55.5)	17.40（13.55-21.98）	0.192
≥25g /d	741(44.5)	16.69（13.52-21.12）	0.192
Whole grains
<25g /d	1072(64.3)	16.96（13.50-21.10）	0.048
≥25g /d	595(35.7)	17.40（13.60-22.31）	0.048
Tubers
<25g /d	942(56.5)	16.98（13.57-21.21）	0.622
≥25g /d	725(43.5)	17.25（13.52-21.71）	0.622
Milk and yogurt
<200mL /d	800(48.0)	16.49（13.01-20.86）	0.001
≥200mL /d	867(52.0)	17.42（13.81-22.00）	0.001
Eggs
<50g /d	1080(64.8)	16.73（13.29-21.15）	0.010
≥50g /d	587(35.2)	17.60（14.03-22.00）	0.010
Livestock meat
<100g /d	820(49.2)	16.91（13.49-21.40）	0.285
≥100g /d	847(50.8)	17.10（13.60-21.50）	0.285
Poultry meat
<50g /d	823(49.4)	17.03（13.57-21.18）	0.615
≥50g /d	844(50.6)	17.09（13.50-21.73）	0.615
River fish, shrimp and crab
<25g /d	1151(69.0)	16.80（13.35-21.15）	0.034
≥25g /d	516(31.0)	17.47（13.89-22.18）	0.034
Sea fish, shrimp and crab
<25g /d	1347(80.8)	17.04（13.49-21.22）	0.344
≥25g /d	320(19.2)	17.08（13.93-21.98）	0.344
Soybeans and Soy products
<25g /d	877(52.6)	16.81（13.20-21.14）	0.058
≥25g /d	790(47.4)	17.26（13.78-21.70）	0.058
Nuts and seeds
<10g /d	1004(60.2)	17.11（13.60-21.13）	0.598
≥10g /d	663(39.8)	16.92（13.40-22.00）	0.598
Dark vegetables
<100g /d	881(52.8)	16.80（13.57-21.05）	0.079
≥100g /d	786(47.2)	17.46（13.50-22.00）	0.079
Light color vegetables
<50g /d	710(42.6)	16.81（13.51-21.09）	0.165
≥50g /d	957(57.4)	17.30（13.59-21.81）	0.165
Mushrooms
<25g /d	1053(63.2)	17.01（13.59-21.32）	0.693
≥25g /d	614(36.8)	17.20（13.50-21.69）	0.693
Fruits
<100g /d	832(49.9)	16.99（13.44-21.18）	0.175
≥100g /d	835(50.1)	17.10（13.62-21.60）	0.175
Puffed foods
<25g /d	1269(76.1)	17.27（13.70-21.52）	0.076
≥25g /d	398(23.9)	16.53（12.98-21.20）	0.076
Sweets
<10g /d	926(55.5)	17.53（13.72-22.00）	0.007
≥10g /d	741(44.5)	16.40（13.24-21.02）	0.007
Sugary drinks
<100mL /d	910(54.6)	17.43（13.65-21.37）	0.124
≥100mL /d	757(45.4)	16.48（13.30-21.57）	0.124
Took calcium or vitamin D supplements within 3 months
Yes	132(7.9)	18.81(15.19-23.31)	0.005
No	1535(92.1)	16.96(13.50-21.36)	0.005

¹ Serum 25(OH)D₃ levels were expressed as P₅₀ (P₂₅–P₇₅)

² P value for the nonparametric test

Table3 Multivariate linear regression analysis on screening dietary factors affecting Serum 25(OH)D₃ levels (n=1,667)

Food items	β value	Standard β value	P-value
Refined rice, steamed
<200g /d	ref	ref	ref
≥200g /d	0.030	0.042	0.091
Refined rice, porridge
<50g /d	ref	ref	ref
≥50g /d	0.016	0.023	0.341
Refined wheat products
<50g /d	ref	ref	ref
≥50g /d	-0.012	-0.018	0.474
Desserts
<25g /d	ref	ref	ref
≥25g /d	-0.007	-0.010	0.718
Whole grains
<25g /d	ref	ref	ref
≥25g /d	0.017	0.025	0.349
Tubers
<25g /d	ref	ref	ref
≥25g /d	-0.005	-0.007	0.772
Milk and yogurt
<200mL /d	ref	ref	ref
≥200mL /d	0.053	0.079	0.002
Eggs
<50g /d	ref	ref	ref
≥50g /d	0.013	0.019	0.452
Livestock meat
<100g /d	ref	ref	ref
≥100g /d	-0.001	-0.002	0.944
Poultry meat
<50g /d	ref	ref	ref
≥50g /d	-0.013	-0.020	0.460
River fish, shrimp and crab
<25g /d	ref	ref	ref
≥25g /d	0.032	0.044	0.135
Sea fish, shrimp and crab
<25g /d	ref	ref	ref
≥25g /d	-0.022	-0.026	0.372
Soybeans and Soy products
<25g /d	ref	ref	ref
≥25g /d	0.012	0.019	0.498
Nuts and seeds
<10g /d	ref	ref	ref
≥10g /d	-0.011	-0.016	0.550
Dark vegetables
<100g /d	ref	ref	ref
≥100g /d	0.001	0.002	0.946
Light color vegetables
<50g /d	ref	ref	ref
≥50g /d	-0.003	-0.005	0.859
Mushrooms
<25g /d	ref	ref	ref
≥25g /d	-0.022	-0.031	0.251
Fruits
<100g /d	ref	ref	ref
≥100g /d	0.032	0.047	0.067
Puffed foods
<25g /d	ref	ref	ref
≥25g /d	0.003	0.004	0.872
Sweets
<10g /d	ref	ref	ref
≥10g /d	-0.035	-0.052	0.048
Sugary drinks
<100mL /d	ref	ref	ref
≥100mL /d	-0.025	-0.037	0.157
Taken calcium or vitamin D supplements within 3 months
No	ref	ref	ref
Yes	0.066	0.053	0.027

¹ Serum 25(OH)D3 levels were expressed as P₅₀ (P₂₅–P₇₅)

² P value for the nonparametric test

Table 4 Serum 25(OH)D3 levels in different physical activity and BMI categories (n=1,667)

Variables	N (%)	25(OH)D₃(ng/mL)¹	P-value²
Total hours of vigorous physical activity per week
<1 hour/day	648(38.9)	17.00（13.25-20.75）	<0.001
1~<2 hour/day	543(32.6)	16.40（13.21-21.29）
≥2 hour/day	476(28.6)	17.78（14.40-22.80）
Total hours of moderate physical activity per week
<1 hour/day	994(59.6)	17.04（13.52-21.46）	0.440
1~<2 hour/day	406(24.4)	17.21（13.72-21.60）
≥2 hour/day	267(16.0)	16.98（13.23-21.36）
Average walking time per day
<30 min/day	588(35.3)	17.70（13.90-22.40）	0.188
30~<60 min/day	622(37.3)	16.80（13.48-20.80）
≥60 min/day	457(27.4)	15.75（13.20-19.96）
Average time of outdoor activity per day
<30 min/day	517(31.0)	16.42（13.11-20.74）	<0.001
30~59 min/day	527(31.6)	16.19（12.92-20.84）
≥60 min/day	623(37.4)	17.97（14.56-22.60）
BMI categories ³
<18.5	390(23.4)	16.25(13.10-20.49)	0.001
18.5~<24.0	906(54.3)	17.05(13.60-21.17)
24.0~<28.0	225(13.5)	18.08(14.13-23.12)
≥28.0	86(5.2)	17.93(14.54-22.30)

¹ Serum 25(OH)D₃ levels were expressed as P₅₀ (P₂₅–P₇₅)

² P value for the nonparametric test

³ 60 data missing in variable BMI

Table 5 Effects of diet, physical activity and UV protection on serum 25(OH)D₃ levels ((n=1,667))

Variables	β value	Standard β value	P-value
Milk and yogurt intake
<200mL /d	ref	ref	ref
≥200mL /d	0.054	0.080	0.001
Sweets intake
<10g /d	ref	ref	ref
≥10g /d	-0.040	-0.059	0.012
Taken calcium or vitamin D supplements within 3 months
No	ref	ref	ref
Yes	0.067	0.054	0.022
Total hours of vigorous physical activity per week
<1 hour/day	ref	ref	ref
1~<2 hours/day	-0.009	-0.013	0.631
≥2 hours/day	0.011	0.015	0.598
Average time of outdoor activity per day
<30 mins/day	ref	ref	ref
30~59 mins/day	0.014	0.019	0.498
≥60 mins/day	0.072	0.103	<0.001
BMI categories
<18.5	-0.011	-0.014	0.571
18.5~<24.0	ref	ref	ref
24.0~<28.0	0.040	0.041	0.094
≥28.0	-0.008	-0.005	0.835
UV protection index	-0.006	-0.064	0.017

Diet, Physical Activity, and UV Protection Comprehensively Influenced Vitamin D Status: A Cross-Section Study of Chinese College Students

Status:

Version 1

Abstract

Figures

1. Background

2. Methods

2.1 Participants

2.2 Questionnaire Survey

2.3 Serum Vitamin D Determination

2.4 Statistical Analyses

3. Results

3.1 Basic characteristics of the participants

3.4 Serum 25(Oh)d Levels In Different Uv Protection Categories

4. Discussion

5. Conclusions

Abbreviations

Declarations

References

Tables

Status:

Version 1