Impact of Seasonal Variation in Association with Other Factors on Vitamin D Status among Mangalorean Population

Abstract

BACKGROUND India has plenty of sunshine, yet people here are deprived of vitamin D – ‘sunshine vitamin’. According to endocrine society of India, vitamin D levels of < 20 ng / mL is considered to be vitamin D deficiency. The objective of the study was to evaluate seasonal variation of vitamin D and give an insight on risk factors such as age, gender, diet, body mass index, occupation, skin complexion and body surface area exposure on vitamin D level. METHODS The study was conducted in a tertiary hospital in Mangalore on 109 apparently healthy individuals. The same cohort of subjects was followed for two seasons - summer and winter. Serum was collected and analysed for 25-OH vitamin D, calcium and phosphorous. Skin color was assessed according to the Fitzpatrick classification, questionnaire was given to assess the approximate time limit of sun exposure in a day along with the exposed areas to sunlight and anthropometric parameters such as height and weight were measured using standard guidelines. Body mass index (BMI) was calculated. Comparison of mean vitamin D along with the factors influencing them in both seasons was done using paired t test. Inferential statistical analysis was done using chi-square test. Pearson correlation test was also done. Statistical significance was considered at P < 0.05. RESULTS Mean vitamin D was higher in summer (15.14 ± 5.62) as compared to winter (14.42 ± 5.38) irrespective of the risk factors. Vitamin D deficiency was highest in older age group (83.9 %), females (84.6 %), overweight (100 %), vegetarians (92.3 %), office workers (91.2 %), both complexions and those exposed with < 1.5 hours of sunlight (97.2 %). Vitamin D deficiency was also more prevalent in those with lesser exposed body surface area. CONCLUSIONS Vitamin D deficiency was statistically most common in winter than summer. It was seen correlating with majority of the risk factors, except skin complexion and among the confounding factors. The key for vitamin D production in this population was maximum body surface area exposure (face, hand, leg and feet) to sunlight for more than 2.5 hours, yet these subjects were vitamin D deficient. However, they did not manifest with any skeletal or extra-skeletal morbidity. Thus, concluding that a reliable cut off value for reference range of vitamin D should be set in this population in order to abstain from excess vitamin D treatment. KEY WORDS Sunshine Vitamin, Vitamin D Deficiency, Mangalore, Skin Colour, Sunlight Exposure, Body Surface Area, Summer, Winter