Health Problems Linked to Vitamin D Deficiency

Man framing sun with hands.
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Despite its name, vitamin D is actually a prohormone, a substance that the body converts into a hormone, usually through sunlight. Vitamin D can reduce your blood pressure, decrease inflammation, and boost the immune system—with benefits ranging from lowering your risk of heart disease and helping your bones absorb calcium to potentially fending off cancer.

That said, nearly 50% of the world suffers from vitamin D deficiency, defined as having less than 20 nanograms per milliliter of the vitamin. This deficiency can manifest in a number of health problems, but there are ways to counteract low levels, from more time outdoors to consuming more foods naturally rich in vitamin D.

How Your Body Makes Vitamin D

Sunlight (specifically UV-B radiation) hits your skin and reacts with specific chemicals (7-dehydrocholesterol) to start making vitamin D. How much time you need in the sun depends largely on where you're located and your pigmentation. Someone in Boston may need one hour in the winter, while a person in Miami during the same time of the year likely needs just 15 minutes.

Vitamin D2 vs. D3

Two major forms of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), the latter of which is used in most supplements. While the two are nearly identical, research has shown that D2 can be less potent in high doses.

Who Is Deficient?

The most at-risk populations include anyone who spends a lot of time indoors (the elderly and the homebound, for example), people with dark skin (darker skin absorbs less sunlight), and those with HIV (the medications amplify vitamin D deficiency).

How a Vitamin D Deficiency Affects Your Body

A number of studies have researched the different ways a lack of sufficient vitamin D can impact the body, including:

Various studies have also investigated the possible link between vitamin D deficiency and rheumatic diseases like arthritis. For example, a 2018 study of 100 people with rheumatoid arthritis found that 84% had low levels of vitamin D compared to the control group. They believe that vitamin D provides an anti-inflammatory response that can reduce the growth of autoimmune disease-related cells, as well as type 1 diabetes and inflammatory bowel diseases.

Some correlations can be made, too. Research has also shown that more heart attacks occur in the winter (when people go outside less and therefore have lower vitamin D levels) and that people survive cancer better in the summer (when their vitamin D levels are higher).


Many older adults have vitamin D deficiencies. Understanding that skin synthesizes less vitamin D as we grow older, a 2014 study analyzed nearly 2,500 people living in an elderly-specific community to see what effect sunlight could have on vitamin D levels. They found that concentrations were much higher in people who regularly took part in outdoor activities like cycling and gardening, compared to those who stayed inside for gym workouts and dancing.

But not all outdoor activities are created equally—they concluded that brisk walking outdoors failed to significantly increase levels of vitamin D. These findings were consistent regardless of other factors like body mass index.

Risk of Death

Many studies have investigated the potential link between vitamin D deficiency and mortality. A 2009 review of nearly 100 studies and trials found a link between low levels of vitamin D and death stemming from all causes, particularly cardiovascular disease, cancer, and respiratory disorders. Researchers believe there are multiple factors that contribute to vitamin D's importance:

  • Boosts cellular growth and immune functions
  • Has nearly 3,000 receptor binding sites, which help regulate a vast number of genes
  • Correlates to longer leucocyte telomere length, a possible marker of longevity and healthy aging

Where You Can Get Vitamin D

There are three main sources of vitamin D, some of which are more reliable than others:

  • Food: Nuts as well as fatty fish like salmon, swordfish, and cod liver oil are great dietary sources of vitamin D. Cheese, eggs, mushrooms, and beef liver have smaller amounts of vitamin D. You can also look for cereals and dairy products fortified with vitamin D.
  • Supplements: Since they're not regulated by the FDA, navigating the supplement aisle (and dosage) can be confusing. While some researchers champion its bioavailability, other studies found little correlation between vitamin D supplements and bone density. Keep in mind that on the flip side, high levels of vitamin D can be unhealthy, leading to conditions like hypercalcemia, high calcium levels that can lead to muscle cramping, dehydration, and kidney stones.
  • Sunlight: To obtain vitamin D from sunlight, spend a little time outside each day—even just exposing your hands and face during that time can be enough. That said, too much time in the sun can lead to overexposure or worse, skin cancer, so make sure to wear sun protection via clothing and SPF.

Tips for Getting More Sunlight

If you work in an office building and live in a neighborhood where you drive everywhere, finding time during the week to be outside is a real challenge. Try a short walk at lunch, which combines the health benefits of walking with vitamin D. Or park further from your entrance and enjoy a longer walk. You can also find an outdoor spot to make a few phone calls during the day.

The Bottom Line

Before you make big changes, consider having your doctor run tests on your vitamin D levels. If there's any concern, you can spend more time outdoors (safely), incorporate vitamin D-rich foods, and discuss the option of a supplement with a professional.

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Article Sources

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