Most people should be able to get their vitamin D requirements met through calculated sunlight exposure. The truth is, however, that our world still has nearly one billion people who are vitamin D deficient, so we’re not getting enough of this sunshine vitamin.
There are various reasons for not getting enough vitamin D. A person’s occupation, age, sunscreen use, geographic location, the time of day, a person’s melanin content and even smog can directly affect vitamin D levels.
In fact, when those who are 70+ in age are exposed to the same amount of sunlight as a young adult, they produce 30% less vitamin D than a younger person. Similarly, those with dark skin need 5-10 times longer sun exposure to make the same amount of vitamin D as those with lighter skin do. Sunscreens may be one of the biggest culprits of all, however, because SPF 8 and above sunscreens can reduce vitamin D production by 95%.
Where you live can have a lot to do with how much vitamin D you can get from the sun, too. If you live north of an imaginary line that stretches from the northern border of California and Boston, then the ultraviolet (UV) energy is not enough for vitamin D synthesis from November through February. The more north you live, the worse it gets. Diminished UV energy can last for up to six months for those areas.
Here are some stats that seem to tell the tale of northern living and vitamin D deficiency:
- 48% of light-skinned girls aged 9-11 in Maine are vitamin D deficient at the close of winter, with 17% of them still vitamin D deficient at the close of the summer.
- Boston has its fallout, too, as 42% of adolescents and 32% of young adults are vitamin D deficient.
- Of the community-living elderly in Boston and Baltimore, 50% are vitamin D deficient throughout the entire year.
- Hospitalized and institutionalized individuals fare even worse: 57% of them are deficient in vitamin D.
If, however, you live south of an imaginary line between Los Angeles and Columbia, South Carolina, then you are among those whose exposure to UV energy allows for vitamin D synthesis throughout the year. But that’s only if you go out in it and if there’s no cloud cover, smog, or any other factor that can inhibit vitamin D absorption.
The truth is that even cloud cover has a hand in how much vitamin D you can get from the sun. Complete cloud cover can reduce UV energy by 50%, while shade—and that includes manufactured shade from pollution, such as smog—slows down UV energy by 60%.
For those who love the sun and want to get their vitamin D levels from it, vitamin D researchers suggest about 5-30 minutes in the sun between 10 a.m. and 3 p.m. at least two times a week to the face, arms, legs or back without sunscreen. This can usually supply sufficient vitamin D synthesis for most people.
Those who don’t get enough sunshine, however, are encouraged to get more dietary sources of vitamin D or to supplement with vitamin D—especially vitamin D3, a preferred form of vitamin D. Vitamin D, as a matter of fact, has two forms especially important to human health: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Be careful what foods you select, too. Some believe they can get adequate vitamin D intake from fortified milk, but milk samples indicate that vitamin D content in milk is highly variable. Less than 50% of sampled milk had at least 50% of the vitamin D content specified on the label, while less than 20% of skim milk had no detectable vitamin D.
And while fatty fish like salmon and mackerel provide natural sources of vitamin D, farmed salmon provides only 10% to 25% of the vitamin D content compared with wild salmon.
So how much vitamin D should we get? Kids from birth to their teen years and adults aged 51 to 70 should get at least 400IU daily, while those 71 and up should get at least 600IU daily. The Institute of Medicine, the government advisory group setting these dietary guidelines, may change recommendations due to emerging research indicating we could require much more—to the tune of 1,000 to 2,000IU daily.
What happens when someone has a vitamin D deficiency?
It often involves getting 50,000IU of vitamin D2 (less for vitamin D3) once a week for eight weeks, followed by 50,000IU of vitamin D2 (less for vitamin D3) twice a month, to compensate for the backlog. That translates into 10,000IU of vitamin D daily for six months to adequately restock the reserves.
The bad news is that many of us aren’t getting enough vitamin D from the sun and other sources.The good news is that we can still get this sunshine vitamin—even on a cloudy day.