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LETTERS TO THE EDITOR
Year : 2018  |  Volume : 22  |  Issue : 6  |  Page : 854-855

Exposure to sunlight and Vitamin D synthesis


Department of Diabetes and Endocrinology, Fortis Hospital, Bannerghatta Road, Bengaluru, Karnataka, India

Date of Web Publication4-Dec-2018

Correspondence Address:
Srinivasa P Munigoti
Consultant Endocrinologist, Department of Diabetes and Endocrinology, Fortis Hospital, 154/9, Bannerghatta Road, Opposite IIM-B, Bengaluru - 560 076, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijem.IJEM_406_18

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How to cite this article:
Munigoti SP. Exposure to sunlight and Vitamin D synthesis. Indian J Endocr Metab 2018;22:854-5

How to cite this URL:
Munigoti SP. Exposure to sunlight and Vitamin D synthesis. Indian J Endocr Metab [serial online] 2018 [cited 2018 Dec 16];22:854-5. Available from: http://www.ijem.in/text.asp?2018/22/6/854/246840



Sir,

I read with interest, an article by Patwardhan et al.[1] published in your journal. It is commendable to note that the authors have put in effort to validate questionnaire to estimate sunlight exposure and then correlate the same with vitamin D status. But authors mention ‘Nevertheless, the association of UV exposure with serum 25(OH)D concentrations in Asian adults from tropical climates like India, where angle and latitude are favourable for receiving optimal sunlight, has to the best of our knowledge not been reported so far’ which is far from truth.

A study from south Indian city, Tirupati (latitude 13.40° N and longitude 77.2° E) using in vitro ampoule model with precursors of vitamin D (7-dehydrocholesterol) when exposed to sunlight demonstrated best conversion to active vitamin D between 11 A.M. to 2 P.M. clearly proving the efficacy of sunlight in vitamin D synthesis. The median percentage conversion of 7-dehydrocholesterol to pre-vitamin D3 and its photoproducts and percentage of pre-vitamin D3 and vitamin D3 was shown to be 11.5% and 10.2% respectively at a solar zenith angle of 36.8° and at 12:30 P.M.[2]

Vitamin D surveys from rural south India (Tirupati) by Harinarayan et al.,[3] have similarly demonstrated higher vitamin D levels in agricultural workers who are exposed to long hours of sunlight as part of their work compared to urban dwellers (~24 ng/mL vs 19 ng/mL) establishing positive correlation between exposure to UV rays from sun and serum vitamin D levels.

In another study from north India,[4] authors compared serum 25(OH) D and bioavailable 25(OH) D in males with varying durations of sun-exposure between indoor and outdoor environments in Delhi during August–September. They demonstrated that serum 25(OH)D increases by 2.03 ng/mL per hour of sun-exposure (95% confidence interval 1.77–2.28; P < 0.001). Also they found that outdoor workers with prolonged sun-exposure were vitamin D-sufficient, with higher serum bioavailable 25(OH) D than the indoor workers during summer.

Studies from Pune (latitude 18.31° N and longitude 73.55° E) involving current authors,[5] themselves have shown that toddlers (of course not adults in this case) exposed to sunlight (playing outside) for more than 30 min a day exposing more than 40% of their body surface area have a normal vitamin D status (males: 91.6 nmol/L and females: 67.7 nmol/L) which was three times more compared with the toddlers who were indoors for most part of the day (males: 32 nmol/L and females: 21.1 nmol/L.[5] A similar association is proven across India in adolescent school children aged 10–15 years by Marwaha et al.[6]

In a dose–response study by Mark et al.,[7] healthy adults of South Asian ethnicity (n = 60; 20–60 years old) while wearing casual clothes that revealed a 35% skin area were exposed to ultraviolet rays equivalent to 15–90 min unshaded noontime summer sunlight at 53.5° N (Manchester, United Kingdom), three times/week for 6 weeks. They demonstrated that participants who received exposures equivalent to 45 min unshaded sunlight (n = 33) attained a mean (±SD) rise in 25(OH) D concentration of 8.7 ± 5.7 ng/mL (95% CI: 6.8, 10.6 ng/mL; P < 0.001), and 94% of subjects achieved concentrations >10 ng/mL proving an association between sunlight exposure and vitamin D status.

I think the association between sunlight exposure and vitamin D synthesis is well established in south Asians especially Indians. Hence, author's claim of novelty of data presented with regards to this association is not true and is ill-founded.

Financial support and sponsorship

None.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Patwardhan VG, Mughal ZM, Chiplonkar SA, Webb AR, Kift R, Khadilkar VV, et al. Duration of casual sunlight exposure necessary for adequate vitamin D status in Indian Men. Indian J Endocrinol Metab 2018;22:249-55.  Back to cited text no. 1
    
2.
Harinarayan CV, Holick MF, Prasad UV, Sreevani P, Himabindu G. Vitamin D status and sun exposure in India. Dermatoendocrinol 2013;5:1-12.  Back to cited text no. 2
    
3.
Harinarayan CV, Ramalakshmi T, Prasad UV, Sudhakar D. Vitamin D status in Andhra Pradesh: A population based study. Indian J Med Res 2008;127:211-8.  Back to cited text no. 3
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4.
Goswami R, Saha S, Sreenivas V, Singh N, Lakshmy R. Vitamin D-binding protein, vitamin D status and serum bioavailable 25(OH) D of young Asian Indian males working in outdoor and indoor environments. J Bone Miner Metab 2017;35:177.  Back to cited text no. 4
    
5.
Ekbote VH, Khadilkar AV, Mughal MZ, Hanumante N, Sanwalka N, Khadilkar VV, et al. Sunlight exposure and development of rickets in Indian toddlers. Indian J Pediatr 2010;77:61-5.  Back to cited text no. 5
    
6.
Marwaha RK, Yenamandra VK, Sreenivas V, Sahay R, Baruah MP, Desai A, et al. Regional and seasonal variations in ultraviolet B irradiation and vitamin D synthesis in India. Osteoporos Int 2016;27:1611-7.  Back to cited text no. 6
    
7.
Mark DF, Ann RW, Richard K, Marie TD, Donald A, Annie H, et al. Efficacy of a dose range of simulated sunlight exposures in raising vitamin D status in South Asian adults: Implications for targeted guidance on sun exposure. Am J Clin Nutr 2013;97:1210-16.  Back to cited text no. 7
    




 

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