I was recently asked “How much is Vitamin D production reduced by increased skin pigmentation?”
I’ve been searched for a while in hopes of finding a more accessible source, unfortunately I haven’t found a review of the evidence that is as thorough as the one in Dietary Reference Intakes for Calcium and Vitamin D (2011), starting on page 101 (http://www.nap.edu/…/dietary-reference-intakes-for-calcium-…), in the section “Effect of skin pigmentation on synthesis”. The short answer to the question seems to be that, in comparing individuals with the least pigmentation to individuals with the most pigmentation, there can up to twice as much production of Vitamin D in the individuals with the lightest pigmentation, but that there is not a linear relationship between skin tone and Vitamin D production, meaning that you cannot predict Vitamin D production based upon skin tone alone (page 102). This is due to the other factors, including genetics which influence an individual’s ability to produce Vitamin D. Also interesting to note, from the same link above on page 106, is that low Vitamin D levels in African Americans are not related to with increased risk of bone fractures as they are for other ethnic groups. Why this is the case seems to be an area that is still being studied.
All that said, the Recommended Daily Allowance for Vitamin D is 600 IU/day for everyone from 1 year of age to 70, and 800 IU for those seventy and older. There are no separate recommendations based upon ethnicity or skin tone. I find a lot of variation in recommendations for sun exposure, and lot of hesitancy to recommend sun exposure due to concerns about skin cancer, but a fairly recent article from the Harvard Medical School relating to bone health and vitamin D (http://www.health.harvard.edu/…/two-keys-to-strong-bones-ca…) says that 5-30 minutes outdoors in the sun twice a week with your face, arms, legs or back exposed is sufficient.