Hello sunshine: the vitamin D story

After a long, cold winter, the first signs of spring come as a welcome relief. Basking in the warm glow, the sunshine on our skin doesn’t just feel good, it is good. Our bodies are absorbing ultraviolet light to make a vital nutrient—vitamin D.

So what do vitamins actually do?
Video by National Geographic

Hello sunshine: the vitamin D story

After a long, cold winter, the first signs of spring come as a welcome relief. Basking in the warm glow, the sunshine on our skin doesn’t just feel good, it is good. Our bodies are absorbing ultraviolet light to make a vital nutrient—vitamin D.

So what do vitamins actually do?
Video by National Geographic

At the turn of the 20th century, medicine recognized only three essential nutrients in food: protein, carbohydrates, and fat. Then, in 1911, Polish biochemist Casimir Funk coined the term vitamine to describe other, as then unknown, “accessory substances.” Research progressed and in throughout the early 20th century a series of essential organic compounds were discovered and labeled alphabetically: vitamins A, B, C, and D.

Vitamins are essential for normal growth and nutrition. Although not themselves a source of energy or a raw material for tissue building, they are crucial facilitators for energy-yielding reactions and metabolic and physiological processes throughout the body—without them, what needs to happen wouldn’t. We only require very small quantities of vitamins, and these come almost exclusively from the foods we eat. Vitamin D is the exception. The few foods that contain it have very low quantities. Instead, unique among vitamins, D is synthesized from sunlight on our skin.

To turn the sun’s ultraviolet rays into something that our bodies can use involves a series of complicated chemical processes. When our skin is exposed to sunlight, it produces vitamin D and directs it to our liver. Here, it is changed into the chemical 25(OH)D and sent to the kidneys, that turn it into activated vitamin D, or calcitriol. It’s the calcitriol that goes to work in our bodies and actually makes things happen, so today vitamin D is often considered to be a hormone rather than a true vitamin.

We are still understanding the full impact it has on our bodies, but essentially it regulates calcium and phosphate to keep bones and teeth healthy. As early as the 1800s, sunlight was being linked to healthy bones following studies into the prevalent bone-deforming disease, rickets. This causes children to develop soft, thin, and brittle bones, and by the end of the 19th century as much as 90 percent of children living in polluted and sunless urban environments suffered from rickets. Ultimately it was understood that vitamin D is the crucial facilitator that allows the body to absorb calcium and phosphorus, the minerals essential for developing the structure and strength of bones and teeth. No matter how much calcium and phosphorus you consume, without vitamin D your body won’t get the benefit.

Beyond bones and teeth, recent research suggests that it might have a positive role in a number of other key systems, supporting healthy cardiovascular function, muscular function, the immune system, endocrine system, and nervous system, as well as playing a role in cell to cell communication. While the symptoms of vitamin D deficiency are often subtle—achy muscles, weakness, bone pain, and brittleness—it has been linked to asthma, diabetes, depression, Alzheimer’s, high blood pressure, multiple sclerosis, and even cancer. This gives vitamin D a role in preventing and treating some of the world’s most serious, long-term health issues: With a certain degree of hype, it’s been touted as a super-vitamin.

In 1941, as the United States went to war, one-third of new recruits were found to suffer from nutritional deficiencies. This prompted the first set of government-sponsored nutrient intake recommendations for vitamins, including D, and the Recommended Dietary Allowance (RDA) was later introduced. Deficiencies continue, however, and today more than 90 percent of Americans fall short on at least one essential vitamin or mineral. Although not as pronounced as in the past, these deficiencies are having a significant impact on the health of millions. It’s estimated that as many as one billion people are vitamin D deficient—that’s 12 percent of the global population.

There are several reasons for not getting enough, but first among them is lifestyle. Whereas once we may have spent the summer outside, modern life means many of us spend as much as 90 percent of our time inside. And finding a sunny spot in the home or office won’t help, as ultraviolet rays cannot penetrate most glass, so you won’t be making vitamin D—or getting a suntan either!

There are other factors that can influence the amount our body makes, including obesity. Body fat will store much of the vitamin D made by the skin so that there is less available for the body to use. Medications such as steroids, cholesterol-lowering drugs, and some diuretics can inhibit the absorption of vitamin D from the intestines, while people of African, African-Caribbean, or South Asian origin find it harder to produce a sufficient quantity because darker skin contains more of the pigment melanin, which acts as a natural sunscreen.

Fortunately, the solution is as simple as a daily supplement. Soon after its discovery, Casimir Funk invented a process for getting vitamin D-rich cod-liver oil into a palatable sugar-coated pill. Today, vitamin D supplements are one of the most common, though the dosage is a matter of debate. We still don’t know exactly how much sunlight we need to get our quota, or how seasonal variations in the strength of the sun affect its efficiency. This has led experts to recommend doses ranging from 15 micrograms per day to as much as 50 micrograms for adults. Naturally, there’s a lot to be said for spending more time outdoors, and checking with a physician to see if a vitamin D supplement could have a place in the medicine cabinet.

We asked some big questions about living a better life. Discover more about how we can overcome the world’s biggest challenges at natgeo.com/questionsforabetterlife

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