The sun is getting stronger and the days are getting longer, even here in Wisconsin.
Some people are coming to the office with nice tans obtained by sunning themselves for several hours. Others have come back from winter getaways to Florida, Arizona, or the tropics, also sporting nice, dark tans.
Several people, in fact, were so confident that sunning themselves provided sufficient vitamin D that they reduced their usual dose. Some even stopped their vitamin D altogether.
But, when blood levels of 25(OH) vitamin D were checked, they were virtually all low, sometimes as low as
<20 ng/ml. Yet all had nice tans.
Why does this happen? Why would people with dark tans remain deficient in vitamin D?
One big factor is age : Anyone over 40 years old is fooling themselves if they think that a tan ensures raising vitamin D levels to a desirable range. Also, the more you tan, the more melanin skin pigment accumulates, and the more vitamin D activation in the skin is blocked.
Weight is another factor: Heavier people need more vitamin D, sometimes three- or four-fold more than slender people.
Why does aging result in inefficient skin activation of vitamin D? It seems that, once we are beyond our reproductively useful years, this ticking clock of aging gets triggered. The older we get, the less activation of vitamin D occurs in our skin, the less of the youth-maintaining, disease-preventing benefits of vitamin D we obtain with sun exposure.
The message: Don't rely on a tan to gauge the adequacy of vitamin D. Maybe that works when you're 16 years old, but not at age 50 or 60. There's only one way to know your vitamin D status: a blood level of 25(OH) vitamin D.