Prevalence and Trends of Metabolic Syndrome in Mexican Adults: Data of the National Health and Nutrition Surveys 2006 and 2016

Background: The metabolic syndrome (MetSx) is a group of risk factors interconnected with cardiovascular diseases and type 2 diabetes, major morbidity and mortality causes globally and in Mexico. More than a thousand million individuals in the world were found with MetSx in 2018, and the last national investigation in Mexico on this condition carried out in 2006 registered a prevalence of 49.8% in adults. This study aimed to describe the prevalence of MetSx in Mexican adults, the degree of association with risk factors, and its trends in the period 2006 to 2016. Methods: We gathered and analyzed sociodemographic, clinical, dietary, and physical activity data from 8,626 adults aged ≥ 20 years who participated in the Mexican National Health and Nutrition Survey Mid-way 2016 (ENSANUT MC-2016). To dene MetSx, we used the harmonized diagnosis criteria as the main instrument. Other classication systems were also used to complement our analysis. To identify the prevalence trends of MetSx, we compared information of ENSANUT-2006 with that of ENSANUT-2016. Results: The prevalence of MetSx in Mexican adults was of 60.5% (57.9% in men and 63.2% in women). The proportion of subjects with a least one MetSx component was of 95.3% and with at least two components was of 21.3%. The most frequent combination of three MetSx components was the cluster of abdominal obesity, low HDL-cholesterol, and hypertriglyceridemia (16%). In comparison with the MetSx prevalence reported in ENSANUT-2006, the prevalence of this condition in ENSANUT-2016 increased 15.3%. Conclusions: A high prevalence of MetSx was registered in Mexico in 2016, and an increased trend of this condition during the period 2006 to 2016 was observed. This study shows the necessity to improve prevention and diagnosis programs for MetSx and its components, as well as the need to adopt a healthy lifestyle in the highest risk population in order to achieve corrections and reductions in associated susceptible risk factors.

Data on dietary intake were obtained from a Food Frequency Questionnaire (FFQ), which accounts for seven days of consumption and contains information of 140 foods and beverages. Information derived from this instrument was used to build 21 food and drinks groups [26]. Afterwards, a dietary diversity index (DDI) was generated by multiplying the number of consumed food groups by the number of days they were consumed in a week. Subsequently, the DDI score was divided into quartiles to provide it with interpretability. Additionally, DDI was categorized into quartiles according to its association with MetSx [27].
Physical activity, screen time, and sleep duration The short version of the International Physical Activity Questionnaire (IPAQ) was utilized to evaluate physical activity (PA) levels of the study sample [28]. PA level performed during the last seven days was categorized by using the WHO classi cation: inactive < 150 minutes, moderately active 150-299, and active > 300 [29]. Regarding screen time categorization, minutes per week that individuals spent on tv watching, videogaming, and computer interaction were counted and then divided into three groups: ≤840, 840-1680, and > 1680 minutes/week [30]. Sleep duration per day was self-reported by participants and classi ed following the recommendations of the National Sleep Foundation: 7-9 hours (reference category), < 7 hours, and > 9 hours (risk categories) [31].

Statistical Analysis
The prevalence and con dence intervals (CI 95%) of MetSx were estimated and described considering categories of sex, sociodemographic variables, anthropometric variables, personal history of lifestyle, chronic diseases background, and biomarkers. Same statistical estimators of MetSx components were estimated by sex and age. The prevalence of both MetSx and its components were reviewed, calculated, and compared between 2006 (National Health and Nutrition Survey 2006 [ENSANUT 2006]) [32] and 2016. To control the effect of the change in the population pyramid, the prevalences were adjusted through the indirect method [33] and by using the WHO standard population as reference [34]. Pearson's chi-squared tests were used to compare prevalences among strata and Bonferroni corrections were carried out for multiple comparisons. To maintain the representativeness of the sample nationwide and by strata, an expansion factor was included. A general p < 0.05 value was considered to set the statistical signi cance. All the analyses were performed by using the SVY module for survey designs in Stata version 14 (StataCorp LLC).

Discussion
According to the present study, six out of ten Mexican adults had MetSx. Among its components, AO, hypoalphalipoproteinemia and hypertriglyceridemia were the most frequent ones. These gures are more than twice than those reported worldwide in 2006 (prevalence of MetSx of ≈ 25.0%) [35]. Since both separately and combined AO and dyslipidemias are the most prevalent MetSx components in Mexican adults, which places this population at a high risk of diabetes [36,37] and CVD [38], strengthening its preventive and control strategies is a priority. The information here presented highlights once again the necessity of implementing rigorous plans of action to enhance dietary choices, promote and increase physical activity, and secure access to pharmacological therapies able to counteract weight excess and lipid abnormalities in Mexico.
Implementation of the above-mentioned strategies is crucial especially considering the lifestyle-related epidemiological scenario in the country. According to National Health and Nutrition Survey 2012, some of the most consumed foods such as processed meats and sugary drinks are those that have a high content of saturated fat and/or sugar [26]. In relation to this, it has been described that in Mexican adults the highest contribution to total energy intake came from products high in saturated fat and/or added sugar (16%), and sugar sweetened beverages (9.8%). These products are casually linked to obesity, diabetes, and hypertension, which besides, hypertriglyceridemia, low HDL-c levels, and insulin resistance, are risk factors for MetSx [39]. On the other hand, in the Mexican population the consumption of vegetables is low since only 40% include them in their diet [40]. This fact is associated with an increased risk of having MetSx [41].
There is enough evidence in literature demonstrating that physical inactivity is one of the main risk factors of MetSx [42]. In relation to this behavior, it has been described that 11.4% of Mexican adults reported not performing enough PA in 2006 and this percentage rose to 14.4% in 2016 [43].
The prevalence of MetSx registered and increment of 21% in the 2006-2016 period [44]. This increase could be in part due to the Western lifestyle diffusion, which entails an unhealthy diet [45] and sedentary behaviors [46], but also to other factors such as population ageing. According to the National Institute of Statistics and Geography in Mexico, the median population age ranged from 24 in 2005 to 28 in 2015 [47]. Given that an increasing trend in the prevalence of MetSx is observed as age increases, it is possible that part of this increment in the prevalence is due to the existence of a larger proportion of adults aged > 40 years in 2016 compared to 2006. However, the prevalence of MetSx in each age group was higher in 2016 compared with 2006. For example, in 2006 [4], 67.9% of adults aged ≥ 60 years had MetSx, whereas in 2016 the prevalence was 76.9%. As it was expected, as age increases, the prevalence of its components also increases, except for low HDL-c. For this reason, execution of actions to tackle MetSx must be directed to every age group, but especially it must start at young ages, since one out of two 20 to 49-year-old adults had this syndrome.
Altogether, MetSx elements are associated with a higher risk of diabetes and CVD [48]. Equally important, its components have been separately associated with these diseases [49]. According to the trend analysis carried out in this study, the prevalence of AO, impaired fasting glucose, low HDL-c, and hypertension relatively remained stable between 2006 and 2016. In contrast, the proportion of Mexican subjects who suffered from hypertriglyceridemia increased by 74%, being this the component that explains to a greater extent the observed increase in the general prevalence of MetSx in this period. Further, the prevalence of hypertriglyceridemia in Mexico is higher than in other developing and developed countries, such as India, Nigeria, China, Japan, and the United States [50]. This scenario exposes the need to continue reinforcing health and nutrition policies able to decrease population's triglycerides concentration, such as soda tax since sweetened-sugar beverages consumption is strongly associated with hypertriglyceridemia [51], and an adequate front-of-pack food labeling system that would allow consumers to take more informed dietary choices and diminish purchases and consumption of high-sugar products. Undoubtedly, early diagnosis and treatment through mass health promotion and screening campaigns, enhancements in the health system infrastructure, an improved medical personnel training, and greater accessibility to pharmacological treatments and nutrition counseling are also crucial strategies to diminish the burden of hypertriglyceridemia and the rest of MetSx components.
The main limitation of this study is its cross-sectional design, which did not allow us to establish causal associations. However, the population-based information generated in this investigation is highly essential to continue designing, evaluating, and reformulating strategies to reduce the burden of MetSx in Mexico.

Conclusions
In conclusion, our results con rm that there is a high prevalence of MetSx in Mexico and the trend in the period 2006-2016 increased. Our ndings show the necessity to improve prevention and diagnosis programs for MetSx and its components. Availability of data and material Datasets from ENSANUT are available from the corresponding author on reasonable request.

Competing interests
The authors have declared that they have no competing interests.