Some supplements you can take or leave. Vitamin D is one you should consider taking.

Unlike, say, vitamin C, it’s hard to get enough of through diet alone. And while our bodies can make vitamin D with exposure to the sun’s ultraviolet-B light (hence the “sunshine vitamin” nickname), our indoor lifestyles and our wise use of sunscreen conspire to limit our personal vitamin D production. So, by at least one measure, about 25% of the U.S. population is vitamin D deficient, and another 41% don’t get quite enough. Older people, women, African Americans, and those ages 20-29 are particularly prone to vitamin D deficiency.

At the same time, the evolving science around vitamin D continues to describe the ways getting enough vitamin D helps us stay healthy. What’s increasingly clear is that getting too little vitamin D in childhood – and perhaps well beyond – may boost risk of autoimmune diseases such as multiple sclerosis and even cardiovascular disease in adulthood.

Vitamin D may limit multiple sclerosis damage

Vitamin D is best known for preventing rickets, the childhood bone disorder. That connection led to vitamin D fortified milk and other foods. But more recently, vitamin D’s broader impact on the immune system has been a research focus.

One example is a recent study of patients who had had a single episode of what, if repeated, becomes multiple sclerosis (MS), an autoimmune condition in which the body attacks the protective sheaths surrounding nerve cells. It found that 60.3% of patients given vitamin D supplements for two years had brain and spinal-cord lesions – less than the 74.1% of patients with lesions who had been given a placebo rather than vitamin D.

Dr. Enrique Alvarez, a University of Colorado School of Medicine Neurologist who specializes in MS patients at UCHealth Neurosciences Center – Anschutz Medical Campus, said the study was well designed and that it “highlights the effect that vitamin D may be helpful.” But he added that there was a high degree of disease in both the vitamin D and placebo groups, and that today’s MS drugs have a bigger impact.

“So, vitamin D may reduce disease activity, but I would consider it an add-on to our current therapies,” Alvarez said.

The study corroborated what’s known as the long-recognized “latitude effect” in MS prevalence, Alvarez noted. In northern and southern latitudes where the sun shines less, there’s more MS in a given population.

Vitamin D is most important in childhood

Vitamin D’s impact on immune-system development may be why. In particular, vitamin D is central to the health of the thymus, an immune system organ that’s central to teaching T-cells what’s friend or foe early in life. (The thymus actually shrinks after puberty). A recent study of mice genetically engineered to produce no vitamin D found that their thymuses aged prematurely. That led their immune systems to be more likely to attack the body’s own tissues, which is what happens in autoimmune diseases.

The link between vitamin D deficiency and MS is also why Alvarez and colleagues recommend vitamin D supplements when patients ask what they can do to lower their kids’ risk of getting the disease. (MS is not considered a hereditary disease, but the risk of MS are higher if a parent or sibling has it).

Low vitamin D levels in childhood may also have cardiovascular impacts, another recent study found. The Finnish study had stored blood samples taken from 3,516 kids ages 5 to 15 years old in 1980 and, adjusting for factors such as diet, physical activity, and socioeconomic status, looked at their risk of early-onset atherosclerotic cardiovascular disease in 2018. They found those with low childhood vitamin D levels to have had between 1.5 times and twice the likelihood of cardiovascular disease by the time they were in their mid-fifties.

Addressing vitamin D deficiency is key

Not all research has pointed to vitamin D as a potential benefactor. Dr. Adit Ginde, a University of Colorado School of Medicine Emergency Medicine physician and the school’s vice chair for research, was part of a team that studied vitamin D’s potential to reduce acute respiratory infections. They found a slight benefit, but it didn’t reach the threshold of statistical significance. Similarly, a major trial considering whether vitamin D brought lower incidence of cancer or cardiovascular events found no benefit.

Those results don’t necessarily contradict those of the Finnish study, though, because the vitamin D was given to adults rather than children whose thymuses are busy training T cells. So there’s still much work to be done, Ginde says. For one thing, the Finnish study was observational and would need to be confirmed with clinical trials involving vitamin D supplementation – no easy task given the decades between cause and effect.

“There have been a number of studies that showed an association between vitamin D deficiency, but very few clinical trials that showed that vitamin D supplementation can improve health outcomes,” Ginde said.

Boosting the immune system: How much vitamin D should you take?

The MS study stands out as one of the few that have demonstrated such a link, it’s compelling, he added. It backs a growing sense among researchers that vitamin D’s biggest impacts may have to do with immune function, be it in tamping down autoimmune and inflammatory diseases or preventing infections.

“There are still many unanswered questions that are being tackled,” Ginde said.

In the meantime, even with the summer sun, it may make sense to take a vitamin D supplement to make sure you’re getting enough of it. Those ages 1 to 70 should get 600 IU international units a day; those over 70, 800 IU a day. Supplements typically come in 1,000 IU to 5,000 IU soft gels, with lower doses available as drops for babies, who should get 400 IU a day. There is such a thing as vitamin D toxicity, but it takes sustained, huge doses to get there. The participants in the MS study took 100,000 IU doses one every two weeks without risking it.

Vitamin D may not be a cure-all, but research has found it to be vital to the immune system’s development – and perhaps, in some cases, regulating its worst impulses.