Are you getting enough Vitamin D? Sunlight through glass doesn't count
You can't get adequate UVB exposure sitting indoors or in a car.
Sunlight doesn’t actually “provide” you with Vitamin D. Rather, your body produces Vitamin D when skin is exposed to the sun’s ultraviolet rays, which trigger Vitamin D synthesis.
The liver and kidneys convert this biologically inert form of Vitamin D into biologically active forms the body can use to promote calcium absorption and bone health.
But sunlight consists of both ultraviolet A or UVA, which penetrates deep within the skin layers and can cause premature ageing; and ultraviolet B or UVB, which causes the redness of sunburn.
It’s the UVB rays that trigger the synthesis of Vitamin D.
Many people can derive the Vitamin D that their bodies need through direct exposure to sunlight during the summer months.
As little as 10 minutes a day of sun exposure is typically adequate.
And you can’t get adequate UVB exposure sitting indoors or in a car. Virtually all commercial and automobile glass blocks UVB rays.
As a result, you will not be able to increase your Vitamin D levels by sitting in front of a sunny window, though much of the UVA radiation will penetrate the glass and may be harmful.
Those concerned about low Vitamin D levels can get more of the vitamin through foods.
The best dietary source for Vitamin D is old-fashioned cod liver oil.
Other dietary sources include swordfish and salmon and, to a lesser extent, fortified milk, orange juice and yogurt, as well as sardines canned in oil, egg yolks and fortified cereals.
Dietary supplements are also available.
By Roni Caryn Rabin © The New York Times
This article originally appeared in The New York Times.