Vitamin D has been in vogue lately, with claims that seem to exalt it to panacea status. Some research suggests it can help treat depression and even help prevent Covid-19 (though this claim remains rickety). And many Americans are vitamin D deficient, after all. Does that mean everyone should be popping these supplements?
Vitamin D, also called calciferol, is vital to human health. It improves calcium absorption and keeps bones strong, and helps prevent osteoporosis in older adults. A vitamin D deficiency may cause bones to become brittle or misshapen. Its also thought to reduce inflammation and promote cell growth.
Unfortunately, most Americans are not getting the right amount of vitamin D. A 2022 study showed that almost 41 percent or more than 71,000 U.S.-based participants were vitamin D deficient. The skin produces vitamin D from sunlight, but we can also get it from some foods and supplements. But is there a superior source? Are there any notable differences between vitamin D from sunlight compared to vitamin D supplements? According to experts, there could be a superior way to get in the right amount.
What is vitamin D?
Vitamin D exists in two main forms. Vitamin D2, or ergocalciferol, is found only in foods or supplements. Mushrooms, yeast, and plants produce vitamin D2, and foods like milk are also often fortified with it. Vitamin D3, or cholecalciferol, comes from animal sources like fatty fish, liver, and eggs. Vitamin D3 is also the kind that your body produces from sunlight.
According to the National Institutes of Health (NIH), adults between the ages of 19 and 70 ought to get 15 micrograms (600 IU) of vitamin D every day. The NIH doesn’t specify which type of vitamin D should fulfill the daily recommended intake. Reinhold Vieth, professor emeritus of nutritional science at the University of Toronto, also says there’s no great difference either, though discerning vitamin D2 from D3 seems to make the biggest difference when it comes to treating vitamin D deficiency. One study from 2022 of over 15,000 participants found that injecting vitamin D3 more successfully treated the condition.
How do we make vitamin D from sunlight?
Vitamin D isn’t called the sunshine vitamin for nothing: Our bodies produce vitamin D3 from sunlight. Vieth says our skin absorbs ultraviolet B (UVB) radiation from the sun. UVB are rays with a wavelength of about 290 to 320 nanometers. In the lowest layers of the skin, the stratum basale and stratum spinosum, are concentrations of the compound 7-dehydrocholesterol. The UVB rays alter the atoms’ spatial configuration, changing it into an isomer known as preD3. Vieth writes that finally, the isomer naturally reforms into cholecalciferol or vitamin D3.
The amount of vitamin D our bodies make from the sun varies depending on the weather. It may take longer to get enough sunlight on a cold, cloudy day than on a hot, clear one because the rays must contend with clouds as well as extra layers of clothing. Robert Ashley, an internal medicine doctor at the University of California, Los Angeles Health, estimates it takes about eight to 10 minutes outside at noon in a t-shirt and shorts to hit the vitamin D daily quota. But on a cold winter day when you are bundled up, it could take hours, even at the same time of day.
Is it better to get vitamin D from the sun or supplements?
According to Vieth, the method doesn’t ultimately matter. “Whether you consume physiological amounts of cholecalciferol orally or whether those amounts are produced within the skin makes zero difference,” he says.
The amount of vitamin D3 our bodies produce varies depending on how much time we spend in the sun, whereas taking a single supplement is much easier to dose.
Because UV radiation is also carcinogenic, and things like sunscreen, air quality, temperature, and skin melanin limit vitamin D production, the case for using supplements over the sun may seem clear.
However, Vieth isn’t offering a free pass to become a vampire. There may not be a physiological difference between vitamin D3 sources, but the evidence makes a powerful case for continuing to source it from sunshine — if not for the vitamin, then for many other good things.
“Sunlight provides benefits that are not mediated via vitamin D,” he writes, such as improved blood pressure, mood, and life expectancy. He points to a 2016 prospective longitudinal study from the Journal of Internal Medicine that looked at sun exposure habits and causes of death in more than 29,500 Swedish women over 20 years. This study found that more sun exposure correlated with a longer life expectancy. (While the study adjusted for exercise habits starting in the year 2000, it didn’t gather that data from the outset. So, this correlation could also come from regular exercise, which many people do at least part of the year outdoors.)
This paper concluded that sunlight was so vital to health that avoiding it created a risk factor for death on par with smoking. The study concluded that compared to those who got the most sun exposure, those who avoided the sun had their life expectancy scaled back by 0.6 to 2.1 years.
There is also such a thing as vitamin D overdose, which Vieth says is more likely to occur from supplements. The NIH puts the upper limit at 100 micrograms (4000 IU), which is equivalent to taking 100 times the recommended dosage every day (60,000 IU), and that can result in toxic buildup and kidney issues, like calcium stone formation. Vitamin D toxicity happens rarely — about 4500 cases in the U.S. every year.
So however you ensure you get your vitamin D, it’s still a good idea to go outside and get some sun.
