Vitamin D is the only vitamin humans can acquire without food — albeit with a catch.
It’s only if we manage to squeeze enough time in our hectic, hermetically sealed indoor lives and expose our skin to sunlight that we’ll reap the benefits of vitamin D that way. However, there are plenty of delicious ways to get vitamin D in food and supplements abound.
Despite the lack of large-scale randomized and controlled clinical studies that factor in skin color, geographic location and lifestyle factors such as diet, some researchers say that increased vitamin D intake might help with the following:
Autoimmune disorders like multiple sclerosis (MS)
A number of studies have found that people who get more vitamin D and exposure to the sun have a lower risk of MS, according to the Mayo Clinic. Some studies suggest that vitamin D may also have benefits for people who already have MS.
One collaborative study between researchers at Oxford and three Canadian universities concluded that low vitamin D levels are directly connected to cases of MS. The study covered more than 3,000 families. Experts suggest people in cold climates with little sun should take vitamin D supplements to prevent autoimmune disorders.
Vitamin D helps the body absorb calcium from food, which allows it to build strong bones throughout life. Getting enough vitamin D and calcium can help prevent osteoporosis and bone fractures and prevent falls in older adults, says WebMD. Children need vitamin D to build strong bones as they grow and also to prevent rickets, a rare disease characterized by bowed legs, weak bones and knocked knees. Adding vitamin D to commercial milk in the '30s helped to nearly eliminate the disease, but it still exists occasionally.
However, very high doses of vitamin D don't help bone health. In a 2019 clinical trial published in the journal JAMA, participants who took high doses of the vitamin had decreases in bone density. They took 4,000 or 10,000 International Units (IUs) per day, versus a control group that took only 400 IUs each day. Those who took high doses had significant declines in bone density in both their arms and legs, while those taking the much smaller supplements only had small declines in bone density in their arms.
More and more studies have found vitamin D deficiency as a risk factor for cardiovascular issues such as heart attacks, congestive heart failure, strokes, and other conditions associated with cardiovascular disease, such as high blood pressure and diabetes, according to Johns Hopkins Health.
If you’re not getting enough vitamin D from sunshine or the minimum 600 IUs from supplements and food, you may be increasing your risk for developing high blood pressure, suggests one study in the Journal of Clinical Investigation.
However, a 2019 study has found that taking vitamin D supplements does not reduce the risk of cardiovascular disease. The large-scale study by researchers at Michigan State University found that vitamin D supplements don't decrease the chance of heart attacks, strokes or other major cardiovascular problems.
Preventing certain cancers
Some research suggests that vitamin D deficiencies have been linked to several cancers including breast and bowel. Some studies suggests that vitamin D may prevent certain cancers. For example, a study in the American Journal of Clinical Nutrition concluded, “Improving calcium and vitamin D nutritional status substantially reduces all cancer risk in postmenopausal women.”
However, in the largest-ever randomized clinical trial testing the supplement for cancer prevention in 2018, vitamin D didn't lower the risk of developing cancer, reports the National Cancer Institute. Almost 26,000 people enrolled in the trial. The incidence of invasive cancer was the same for the participants who took vitamin D as for those who didn't.
Studies have found that people who are obese and who have high levels of body fat often have low levels of vitamin D. According to WebMD, body fat traps vitamin D, which makes it harder for the body to use it. Researchers don't know if obesity causes low levels of vitamin D or if it's vice versa. Some limited research has found that adding vitamin D to a healthy, low-calorie diet might help people who have low vitamin D levels lose weight more easily.
Some early studies suggest that people who have dementia also have lower levels of vitamin D. But studies don't make it clear whether taking supplemental vitamin D can prevent dementia or can benefit people who already have the condition, reports WebMD.
Regulating the release of insulin
Some studies have shown a link between low levels of vitamin D and diabetes. For example, researchers at the Institute of Animal Physiology in Munich, Germany, found that mice have vitamin D receptor cells located within insulin-secreting cells of the pancreas and these cells play an active role in the release of the blood sugar-regulating hormone when higher demand calls for its release.
Limited human studies suggest a correlation between low vitamin D levels and insulin secretion and glucose tolerance in individuals with Type 2 diabetes. But there's not enough research for doctors to suggest taking the supplement to prevent or treat diabetes.
There's a lot of inconclusive evidence about many other conditions and how they might be impacted by low levels of vitamin D. Early research shows that there might be a connection between the vitamin and the following conditions, according to WebMD:
- Alzheimer's disease
- Gum disease
- High cholesterol
- Kidney disease
- Premenstrual syndrome (PMS)
- Rheumatoid arthritis
Skin cancer, the sun and vitamin D
According to the journal Cancer, cancer rates are twice as high in the Northeast U.S. as compared to those in the Southwest. The journal concluded in one article that, “many lives could be extended through increased careful exposure to solar UV-B radiation and more safely, vitamin D3 supplementation, especially in non[-]summer months.”
When it comes to balancing getting adequate amounts of vitamin D at the risk of getting sunburned, Dr. Jacob Teitelbaum, author of "Real Cause, Real Cures" suggests, “Just use common sense and don’t be paranoid about being out in the sun.”
Teitelbaum adds, “Historically people spent most of the day outside, weren’t dipped in sunscreen and didn’t have sunglasses on. They got plenty of sunshine. That was the normal way to get vitamin D.”
The Skin Cancer Foundation suggests no more than 10 to 15 minutes of unprotected sun exposure two to three times a week. "That minor amount of exposure produces all the vitamin D your body can muster," writes Dr. Anne Marie McNeill and medical assistant Erin Wesner. The rest of the time, slather on some sunblock and stay safe, they say.
Editor's note: This story has been updated since it was originally published in April 2012.