Current study examined 25(OH)-Vit D levels to determine the prevalence of vitamin D deficiency or insufficiency and also looked into selected associated factors among post-menopausal women with suspected osteoporosis. Bone density assessment was carried out among 77 participants. To the best of our knowledge, this is the first study in the region where Vitamin D status was measured among post-menopausal women even though several studies examined vitamin D level in general population. Gunawardane et.al found that Vitamin D deficiency in Sri Lanka was 57.2% (<20 ng/mL), vitamin D insufficiency 31% (20-30 ng/mL) and the cumulative prevalence of deficiency & insufficiency was 88.2 % (11) and high prevalence was found among young adults (age 18-40) (11). In the present study, the mean 25(OH)-Vit D concentration was 27.5 ng /mL ±8.09ng/mL and 19% (95%CI: 12.4-27.4) had vitamin D deficiency (25(OH)- Vit D concentration <20ng/mL). Overall, we have found that cumulative deficiency and in- sufficiency of vitamin D was common, 63.8% (95%CI: 54.3-72.6). However, a study among 123 postmenopausal women evaluated in Romania reported 91.9% of them had 25(OH)-Vit D levels below 30 ng/mL (16). Likewise, a study done in Pakistan among 200 postmenopausal women presented to Orthopaedics and Gynaecology outpatient departments of Khyber Teaching Hospital showed that prevalence of vitamin D deficiency was 59 % and 22% had insufficient levels (10). Almost similar findings revealed in a study from North India which showed vitamin D deficiency among 62% of subjects (17). Even though, direct comparison among these studies is difficult, relatively low prevalence among our sample could be due to a good exposure to sunlight, a natural source of vitamin D throughout the year as Northern Sri Lanka is located in the tropical region. Historically, most of the requirement of vitamin D is from sun light–induced manufacture of cholecalciferol by skin (7). Seventy-five of participants (71.4%) reported adequate level of sun exposure (30minutes/day). Authors of the study conducted in Pakistan reported that the use of sun protection, wearing purdah and in general women do not go out of their home were possible explanations for low vitamin D levels in their population (10). However, in Sri Lankan culture, there is no cultural restriction for women to go out from their homes or force to fully cover themselves which support our findings.
Many studies have showed an increasing level of vitamin D deficiency with age [18, 19]. The main reason would be that the elders would have decreased concentrations of precursor of vitamin D3 (7-dehydrocholesterol) that leads to decreased ability to make vitamin D by skin . However, in the present study, 25(OH)-Vit D level showed positive correlation with advancing age (r-0.225, P-0.021). Again the amount of sun exposure is a possible factor contributed to this finding. Young women tend to spend more time indoors with their occupation while a traditional house-wife in Jaffna and the elderly spend more time outdoors. This finding was in par with some previous studies (20, 21) and further a study in Thailand showed young people could have used more sunscreen because of cosmetic reasons (20), however this practice was not observed in this study as only two participants (1.9%) reported to use sunscreen. In terms of dietary sources, common non-fortified food sources include breast milk, cod liver oil, egg yolk, fish such Mackerel (canned), Salmon (canned), Salmon (fresh, farmed), Salmon (fresh, wild), Sardines (canned) Tuna (canned), cat fish, yogurt, margarine, cereals and mushroom (1,22). Among 105 participants 53% of them consumed milk on average 3 days per week, 76.2% consumed fish on average 2 days per week, 64.8% consumed egg on average 1 day per week. Nevertheless, no significant difference in 25(OH)- Vit D level was observed between those who consumed vitamin D rich food and those who did not(Table 7). This indicates dietary source not plays a pivotal role.
Vitamin D deficiency symptoms are rather nonspecific which include back pain (non-radiating), arthralgia, proximal muscle weakness, headache, fatigue, altered mood, insomnia and hair loss (23, 24). In our study 57.1% postmenopausal women reported paraesthesia followed by bone pain (55.2%), easy fatigability (54.3%), malaise (51.4%), muscle cramps (43.8%) and proximal myopathy (40.0%). However, there was no statistical significance observed at 5% level when comparing symptoms among groups with 25(OH)-Vit D deficiency and with adequate levels of 25(OH)-Vit D. This could be due to the fact that the symptoms are non-specific and are common in post-menopausal women even without vitamin D efficiency or might also be associated with other age related co morbid conditions such as osteoarthritis. For example, among 105 participants 41.9% had osteoarthritis and 3.8% had rheumatoid arthritis. The study also investigated the relationship between vitamin D deficiency and menopausal symptoms and concluded that the data is not supportive of vitamin D status association with menopause related symptoms (25).
Vitamin D deficiency reported to be high in prevalence among inpatients with mental illness in previous studies (26, 27). Thirty percent of samples had psychiatric conditions and mean 25(OH)-Vit D level (25.63ng/mL) was less among the participants with psychiatric conditions compared to those not having psychiatric conditions (28.68ng/ml). But this results did not show statistically significant difference (P-0.076).
It is well known fact that prevalence of osteoporosis is common among postmenopausal women and several risk factors implicated for this high prevalence includes vitamin D deficiency. Falls and risk of fractures were well associated with vitamin D deficiency among post-menopausal osteoporosis (4). Out of 105 post-menopausal women suspected with osteoporosis 71 (66.7%) completed bone density assessment and results revealed osteoporosis was present in 38% (27.3-49.7) and another 38% showed osteopenia. However, Vertebral T score within osteoporosis range was higher (64.8%) and (33.8%) showed osteopenia. Present study failed to show association with different categories of T scores with vitamin D deficiency except Vertebral Z score which showed a significant correlation with 25(OH)-Vit D level (r-0.252, P-0.034). This results could be due to a small size sample and this study was not designed to show this association (not a comparative study). Nevertheless, it is a well-known fact that vitamin D deficiency is more prevalent among post-menopausal women and supplement of vitamin D might prevent of falls and fractures, particularly with people with osteoporosis (4, 28, 29).
The appropriate cut-off level to treat vitamin D deficiency or insufficiency is a dilemma (8). To maintain minimum required 25(OH)-Vit D level (30 to 32 ng /mL) requires 2,200 to 3,000 IU/day from all available resources including sun exposure, food and supplements (30, 31, 32). Further, age specific recommendations suggest 200 IU of vitamin D daily from birth to age 50, 400 IU/day for age 51 to 70 years, and 600 IU/day for those aged 70 years and above (33,34) This recommendation presume that usual sources of vitamin D such as sun exposure and food are not adequate (31,32). It is an observation that vitamin D supplements for all post-menopausal women may lead to hypervitaminosis D. Still, supplementation with vitamin D for post-menopausal women with vitamin deficiency is beneficial in preventing osteoporosis especially to prevent complications of fall and fracture (11, 16). Since high prevalence of vitamin D deficiency among post-menopausal women with suspected osteoporosis has been shown by this study, it emphasizes the fact that early screening for suboptimal 25(OH)-Vit D level among the above group is crucial to prevent osteoporotic fractures and falls.
The strengths of this study are that this was the first study in Sri Lanka specifically examined the prevalence of vitamin D deficiency among post-menopausal women with suspected osteoporosis and explored some protective factors like sun exposure. 25(OH)-Vit D level measured by competitive immunoassay with enhanced chemiluminiscence technique method which is one of the standard clinical laboratory methods. However, some limitations of the study includes that we did not obtain information about some anthropological measurements such as BMI(Body Mass Index); physical activity; socioeconomic status and the influence of seasonal effects and climatic changes on vitamin D deficiency. Calcium level measurement completed only among 77 participants due financial and social reasons. Furthermore, sample size estimated only with the aim of estimating prevalence but validity of the study would have been improved if we had an estimated sample size for sub analysis. Some participants (33.3%) did not complete bone density assessments which could be the reason for some factors not showing statistically significant association, even though some relationship observed in psychiatric condition, sun exposure, z/t scores of vertebral DEXA and 25(OH)-Vit D level.