What Are the Benefits of Vitamin D?

You may know vitamin D for its role in bone health. But research shows that this fat-soluble vitamin offers more wide-ranging benefits.

“Vitamin D is integral to the endocrine and immune systems, bone health, and metabolism in general,” says JoAnn Manson, MD, MPH, DrPH, a Mass General Brigham endocrinologist and chief of the Division of Preventive Medicine at Brigham and Women’s Hospital.

Dr. Manson is principal investigator on the VITAL study, which is looking at the effects of daily vitamin D supplementation on cancer, cardiovascular disease (CVD), and various other health outcomes. Here, she discusses their recent research published in The American Journal of Clinical Nutrition, along with other benefits of vitamin D and when to consider supplements. 

Slowing biological aging

Vitamin D may slow biological aging by protecting telomeres—the ends of chromosomes—from shortening. Telomeres naturally shorten during aging and cell division, and researchers have linked this process to an increased risk of diseases such as CVD, Alzheimer’s, and multiple sclerosis (MS). 

In their recent study, Dr. Manson and researchers found that people who were given supplements with 2,000 international units (IUs) of vitamin D daily saw significantly less telomere shortening over 4 years than those given placebo. The effect was equal to preventing nearly 3 years of aging.

“It’s an exciting finding, and we’re pursuing it more deeply by exploring vitamin D’s effects on other biological pathways of aging,” Dr. Manson says.

Supporting immune health

Vitamin D reduces inflammation in various ways, offering benefits for immune health. It keeps the immune system from attacking your body’s tissues and helps infection-fighting cells work better.

Dr. Manson explains that by controlling and tamping down inflammation, vitamin D can lower the risk of autoimmune diseases, including:

• Inflammatory bowel disease
• Lupus
• Multiple sclerosis
• Psoriasis
• Rheumatoid arthritis (RA)

Promoting bone health

Vitamin D helps your body absorb calcium, the mineral that builds and maintains bones. In fact, without enough vitamin D, your body would only absorb roughly 10 to 15% of the calcium you consume.

But you shouldn’t take high doses of vitamin D supplements to boost calcium levels. Mega-dosing vitamin D can cause calcium to build up in the blood and urine, Dr. Manson says. Calcium buildup (hypercalcemia) weakens bones and can also lead to kidney stones and hardened arteries. Instead, most people should stick to a dosage of 1,000 to 2,000 IUs of vitamin D per day.

Reducing advanced cancer risk

The VITAL trial also found that high-dose vitamin D supplements (2,000 IUs daily) taken over 5 years reduced the risk of advanced cancer—cancer that has spread or proved fatal—by approximately 20% in people without cancer at the start of the study. In particular, vitamin D seems to protect against advanced cancers linked to inflammation or problems with immune system regulation, Dr. Manson says.

The researchers don’t know exactly why. However, Dr. Manson notes it likely involves the role of vitamin D in reducing inflammation and supporting immune function.

Sources of vitamin D

You can get vitamin D in two ways: diet and sunshine. When sunlight contacts your skin, it triggers the body to make vitamin D. Some researchers suggest that you can get enough vitamin D from just 15 minutes of sun exposure a few times per week. 

Foods high in vitamin D include:

• Beef liver
• Cheese
• Egg yolks 
• Fortified foods (foods with extra nutrients added)
• Salmon

Do I need a vitamin D supplement? 

The National Institutes of Health recommend that adults get between 600 and 800 international units (IUs) of vitamin D per day. Recent guidelines from the Endocrine Society say to consider a vitamin D supplement if you are:

• 1 to 18 years old
• At risk of prediabetes
• Pregnant
• Over age 75

“Although most people are already meeting their requirements for vitamin D and only a small percentage of the population is truly deficient, taking a supplement with 1,000 to 2,000 IUs per day is very safe and can serve as a form of insurance,” Dr. Manson says. 

Other people who may also benefit from a vitamin D supplement include those with digestive conditions that affect the ability to absorb nutrients, such as Crohn’s disease, ulcerative colitis (UC), and celiac disease. And people who live in areas with minimal sun exposure during winter may find it challenging to get enough vitamin D during certain times of year. “That may also be a good time to take a vitamin D supplement,” Dr. Manson says.

She adds one caveat: “Vitamin D supplements will never be a substitute for a healthy diet or lifestyle.” So regardless of what supplements you take, focus on healthy habits like a balanced diet, regular exercise, not smoking, adequate sleep, and stress management.