Published on 12 January 2022
InsHeal wishes its readers a Happy, Healthy and Safe New Year 2022!
Today’s blog is on sunlight as a source of vitamin D, a vitamin that has been a frequent topic of discussion in the past couple of years due to its role in maintaining immunity against the COVID-19 infection.
The role of vitamin D in maintaining bone health is well established. Vitamin D is obtained from two main sources – diet and exposure to sunlight. The skin converts cholesterol into vitamin D when exposed to the ultraviolet B rays from the sun.
Sunlight and Vitamin D – The Best Time to be Outdoors
The best time for sun exposure to promote the production of vitamin D by the skin is between 10 am and 3 pm. During these hours, the skin receives direct ultraviolet B rays. In contrast, during morning and evening hours, the ultraviolet B rays are oblique, the path of light is longer and therefore the amount of rays absorbed by the ozone layer surrounding the earth is more. Therefore, less ultraviolet B light reaches the skin, resulting in a lower production of vitamin D.
An exposure for around 10-15 minutes may produce adequate levels of vitamin D in light-skinned individuals. Too much exposure could damage the skin and predispose to skin cancers, and should therefore be avoided.
Sunlight and Vitamin D – Maximize the Benefit
The skin produces vitamin D only when the sunlight falls on parts that are not covered by textile such as the face, arms, hands and legs. Thus, a short-sleeved shirt may be preferred to a long-sleeved one if the time spent outdoors is limited. Sunscreens can also reduce the production of vitamin D by the skin. Since glass absorbs the ultraviolet B rays, the skin will not produce vitamin D when exposed to sunlight that comes in through closed windows, which stresses on the need to be out under the direct sun.
Sunlight and Vitamin D – Interfering Factors
Some factors that could reduce the ability of the skin to produce vitamin D. In such cases, an increase in the duration of exposure, an increase in the dietary intake or supplementation of vitamin D may be considered. For example, older age and darker skin may reduce the ability of the skin to produce vitamin D. The vitamin D production by the skin may also be reduced by environmental factors such as air pollution, or a residence closer to the poles.
Zhang R, Naughton DP. Vitamin D in health and disease: current perspectives. Nutr J. 2010;9:65. Published 2010 Dec 8. doi:10.1186/1475-2891-9-65
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