Abstract
Summary
Evaluation of ultraviolet B index (UVBI) and its impact on vitamin D synthesis is important. We observed the maximum UVBI between 11 am and 1 pm. There was no increase in serum 25(OH)D levels following sun exposure during winter as the UVBI was significantly low, emphasizing the need for vitamin D supplementation during these months.
Introduction
The amount of vitamin D3 synthesizing UVB irradiation (290–320 nm) reaching the earth’s surface at different altitudes and seasons in different parts of India and it’s impact on vitamin D synthesis has not been well studied.
Methods
The hourly UVB index (UVBI) from 10 am to 3 pm everyday for 12 months was measured by a solar meter in 4 different zones (North, Northeast, West and South) of the country. To study the impact of sun light exposure on vitamin D synthesis during winter, healthy school children aged 10–15 years were exposed to sunlight for a period of 30 min per day, between 11 am to 12 noon with 10 % body surface area, for 4 weeks. The main outcome measures were serum 25(OH)D, PTH, calcium, phosphate, and alkaline phosphatase levels before and after sun exposure.
Results
The mean UVBI was highest between 11 am and 1 pm throughout the year in all locations. The highest UVBI was recorded from the North zone (4.5 ± 2.7 μW/Cm2), while the least was recorded in the Northeast zone (2.1 ± 1.2 μW/Cm2). UVBI readings in the Northeast zone were consistently low throughout the year, while all the other three zones showed significant seasonal fluctuations.
Surprisingly, we observed a significant decrease in serum 25(OH)D levels from baseline (6.3 ± 4.6 to 5.1 ± 2.7 ng/mL; p < 0.001) despite sun exposure.
Conclusion
The mean UVBI was highest between 11 am and 1 pm throughout the year in all locations. No increase in the serum 25(OH)D levels was observed following sun exposure in winter, emphasizing the need for vitamin D supplementation during these months.
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Acknowledgments
We gratefully acknowledge Mustafa Basharat and Deepti Talwar for their help in recording UVB index in Leh and Delhi, respectively.
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Endocrine Society of India
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Marwaha, R.K., Yenamandra, V.K., Sreenivas, V. et al. Regional and seasonal variations in ultraviolet B irradiation and vitamin D synthesis in India. Osteoporos Int 27, 1611–1617 (2016). https://doi.org/10.1007/s00198-015-3427-0
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DOI: https://doi.org/10.1007/s00198-015-3427-0