Vitamin-D deficiency is very common in a country like Bangladesh specially among people who resides in urban areas. Sun avoidance and regular use of sun block might be the etiologic factors. What could be minimum period of sun exposure daily/ weekly to prevent the development of Vitamin-D deficiency?
At first what level are you aiming at. Avoiding deficiency (aiming at about 50 nmol/L) or going towards optimum levels (75 - 125 nmol/L). And at what latitude and time of the year are you looking at? What skin color and what age?
In 2004 Holick wrote (AmJClin Nutr): Sensible sun exposure (usually 5-10 min of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week) and increased dietary and supplemental vitamin D intakes are reasonable approaches to guarantee vitamin D sufficiency.
It's recommended that 5-10 mins of sunlight exposure 5days a week.. preferably between 10am to11am.. is enough to meet the daily need..
I agree with Rachna Pasi questioning the 5-10 minutes, it was also Holick in the old days who wrote this. Presently he advocates higher doses.
Personally (and dependent on the latitude) I prefer 20-30 minutes each day exposure of hand, arm & face between 10 and 16 hrs in summer season.
The total amount of vit D from sun exposure, diet and suppletion should be between 1000 and 2000 iU per day.
Thanks to Jos Wielders for your comment. You have opined sun exposure of hand, arm and face 20-30 minutes daily between 10-16 hours. What might be the amount of Vit-D produced by this sun exposure?
No exact exposure period needed can be calculated, it is highly dependent on many factors.
John Cannell once wrote about this subject:
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As a general rule, the higher the sun is in the sky (solar zenith angle), the more vitamin D is made in the skin. By controlling for solar zenith angle, as you wisely did, you also controlled for factors such as latitude, season and time of day. However, multiple other factors are at play, such as:
There are other factors just being discovered, factors that are difficult for people to gauge. For example, presence or absence of common “mutations” called single nucleotide polymorphism (SNPs) of the vitamin D metabolic machinery.
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Additional literature to read:
- Optimum Sun Exposure Times for Vitamin D Status
Correction in Saudi Arabia ( doi: 10.11648/j.ejpm.20150305.14 )
or Holick reviews
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Have a look at this useful link.
https://ods.od.nih.gov/factsheets/VitaminD-health%20Professional/
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