title: Regional and seasonal variations in ultraviolet B irradiation and vitamin D synthesis in India.
abstract: 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.
  
  
  BACKGROUND
  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/Cm(2)), while the least was recorded in the Northeast zone (2.1 ± 1.2 μW/Cm(2)). 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: International Life Sciences Institute, New Delhi, India.
authors.forename: R K
authors.initials: RK
authors.lastname: Marwaha
authors.affiliation: Department of Dermatology, All India Institute of Medical Sciences, New Delhi, 110029, India.
authors.forename: V K
authors.initials: VK
authors.lastname: Yenamandra
authors.affiliation: Department of Biostatistics, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: V
authors.initials: V
authors.lastname: Sreenivas
authors.affiliation: Department of Endocrinology, Osmania Medical College, Hyderabad, India.
authors.forename: R
authors.initials: R
authors.lastname: Sahay
authors.affiliation: Excel Center, Guwahati, India.
authors.forename: M P
authors.initials: MP
authors.lastname: Baruah
authors.affiliation: Endocrine Unit, Department of Medicine, Goa Medical College, Bambolim Goa, India.
authors.forename: A
authors.initials: A
authors.lastname: Desai
authors.affiliation: Christian Fellowship Hospital, Oddanchatram, Dindigul, India.
authors.forename: S
authors.initials: S
authors.lastname: Kurvilla
authors.affiliation: Christian Fellowship Hospital, Oddanchatram, Dindigul, India.
authors.forename: S
authors.initials: S
authors.lastname: Joseph
authors.affiliation: Chellaram Diabetes Institute, Pune, India.
authors.forename: A G
authors.initials: AG
authors.lastname: Unnikrishnan
authors.affiliation: Department of Cardiac Biochemistry, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: R
authors.initials: R
authors.lastname: Lakshmy
authors.affiliation: Department of Dermatology, All India Institute of Medical Sciences, New Delhi, 110029, India.
authors.forename: C
authors.initials: C
authors.lastname: Apoorva
authors.affiliation: Department of Dermatology, All India Institute of Medical Sciences, New Delhi, 110029, India.
authors.forename: V K
authors.initials: VK
authors.lastname: Sharma
authors.affiliation: Department of Dermatology, All India Institute of Medical Sciences, New Delhi, 110029, India. kgsethu@yahoo.com.
authors.forename: G
authors.initials: G
authors.lastname: Sethuraman
mesh_terms: D000293:Adolescent; D002648:Child; D002762:Cholecalciferol / Q000096:biosynthesis*; D005260:Female; D062305:Geographic Mapping; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D000069079:Radiation Exposure; D012574:Schools; D012621:Seasons; D013472:Sunlight; D014466:Ultraviolet Rays; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology
chemical_list: D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D
keywords: India; Ultraviolet B; Vitamin D