Vitamin D is unique as far as vitamins go.

For starters, one of the best ways to absorb the vitamin is natural sunlight. There’s also the fact that it isn’t found in many foods, aside from fatty fish, egg yolks, or products that have been fortified with the supplement.

In fact, many would argue, vitamin D doesn’t have a lot in common with other vitamins because it’s synthesized by the body.

“Some scientists believe it functions more like a hormone than an actual vitamin because we have so many vitamin D receptors throughout the whole body. A large part of the immune system has vitamin D receptors,” Dr. Todd Sontag, DO, a family medicine specialist at Orlando Health in Florida, told Healthline.

However hard it may be to pin down, there’s no denying the benefits of vitamin D when it comes to bone and muscle health.

“I think it’s a great vitamin,” says Sontag. “It’s one of the few that actually does have some legitimate benefit. A lot of vitamins out there have really good marketing without a lot of science behind them.”

It’s worth noting that vitamin D-3 (the natural version of vitamin D) is included on the World Health Organization’s List of Essential Medicines, a list of medications needed in order for a health system to be safe and effective.

Multivitamins, meanwhile aren’t even recommended by the U.S. Preventive Services Task Force.

The most commonly known positive health outcome associated with good vitamin D levels is bone health.

“The ones that are very evidenced are going to be bone issues,” says Sontag. “As far as bone thinning — osteoporosis, osteopenia, as well as rickets in kids and osteomalacia in adults — those are the ones that are really associated with legitimate vitamin D deficiency, in which case vitamin D helps. Newer evidence shows that it also helps prevent falls and fractures in the elderly, and that’s why the elderly are now supposed to be taking higher doses of vitamin D.”

Vitamin D has long been known for its association with good bone health.

But new research suggests the sunshine vitamin could be effective at warding off a host of other ailments as well.

Here are five of them.

Type 2 diabetes

A study published last month in PLOS One found that people with vitamin D deficiency could face a higher risk of developing type 2 diabetes.

Researchers studied healthy, older adults with no prior warning signs of diabetes or prediabetes. Over a 12-year period, many participants developed diabetes or prediabetes.

Of those participants, it was found that vitamin D deficiency was a strong predictor of whether a participant would develop those complications.

Ultimately, it was found that those with vitamin D levels above 30 nanograms per millilitre had one-third the risk of developing diabetes, while those with levels above 50 nanograms per millilitre had one-fifth the risk.

The study’s authors acknowledged that more research is needed, but that the results show promise.

“Further research is needed on whether high 25-hydroxyvitamin D levels might prevent type 2 diabetes or the transition from prediabetes to diabetes,” said study co-author Cedric F. Garland, adjunct professor in the University of California San Diego (UCSD) School of Medicine Department of Family Medicine and Public Health. “But this paper and past research indicate there is a strong association.”

Muscle strength

Researchers at the University of Birmingham reported last year that higher levels of vitamin D could help optimize muscle strength.

To conduct the study, participants were measured for active and inactive vitamin D levels, along with their overall physical characteristics, such as body fat and muscle bulk.

It was found that increased levels of active vitamin D can promote and optimize muscle strength.

“We found that the receptor which vitamin D is known to act through was present in muscle from our research volunteers,” Zaki Hassan-Smith, PhD, lead study author and clinical lecturer at the Institute of Metabolism and Systems Research at the University of Birmingham in the United Kingdom, told Healthline in an email last year. “We also observed associations between serum vitamin D levels and a number of genes that are involved in muscle function.”

Depression

Since sunlight provides vitamin D and since many people tend to feel more depressed during the low-light winter months, it stands to reason that there’s a connection between vitamin D and depression.

A 2008 study found that increased vitamin D supplements significantly reduced symptoms of depression in overweight and obese people.

A more recent study concluded that people with low concentrations of vitamin D were more likely to be depressed.

Cardiovascular health

A study out of Ohio University earlier this year used high-tech nanosensors to analyze the relationship between vitamin D levels and heart health.

The nanosensors allowed researchers to observe endothelial cells, which line blood vessels and help regulate blood circulation and cardiovascular health.

Various ailments that strain the cardiovascular system, such as hypertension and diabetes, can cause damage to these endothelial cells. Damaged cells in turn carry a higher risk of heart attack.

But the Ohio University researchers found that vitamin D-3 can actually help restore the health and strength of endothelial cells.

While the authors acknowledge that more research is needed, they point out that vitamin D-3 is cheap, accessible, and may be able to do the job better than any other medication that’s currently available.

“There are not many, if any, known systems which can be used to restore cardiovascular endothelial cells which are already damaged, and vitamin D-3 can do it,” said Tadeusz Malinski, study lead author and a professor of chemistry at Ohio University, in a statement.

Dementia and Alzheimer’s

A 2014 study investigated the relationship between vitamin D deficiency and risk factors for different types of dementia, including Alzheimer’s disease.

Researchers looked at more than 1,600 older adults who did not have dementia when the study began.

While vitamin D wasn’t found to be a wonder drug in preventing dementia, researchers did conclude that people who had moderately low vitamin D levels had a 53 percent higher chance of developing dementia compared to those with normal levels.

Among participants with severe vitamin D deficiency, the difference was even more striking, with this group having a 125 percent increased risk.

It was also found that people with low vitamin D levels were 70 percent more likely to develop Alzheimer’s specifically.

Cautious optimism

While the research is promising, experts say it’s important to have measured expectations.

“Vitamin D benefits bone density, and probably a lot of these other things as well, but we just don’t have enough evidence yet,” says Sontag.

Sontag notes that vitamin D deficiency is a common concern.

“I’m in Florida, and I diagnose vitamin D deficiency almost every day,” he says. “I don’t know why we’re not absorbing it well. It shouldn’t really be this widespread. Now that doctors are looking for it, we’re obviously finding it a lot more.”

With the established medical knowledge of vitamin D’s positive impact on bone health, plus the promising research into other ways it impacts health, Sontag says it’s important to make sure you’re getting enough.

“It’s not really in much food and we’re not absorbing it well, so it’s definitely something we should be checking for with bloodwork if we can,” he says. “I think there’s a lot about vitamin D that we don’t know. I really think it’s more important than we realize at this point.”