What Can Vitamin D Really Do for Your Health?

What comes to mind when you think of Vitamin D? You may picture a sunny day on the beach, since our bodies can make Vitamin D with regular exposure to UV rays, or you may think of bone health. But research over the past 15 years suggests that Vitamin D may benefit our bodies in a slew of other ways.

Low levels of Vitamin D are associated with a higher risk of certain cancers; autoimmune diseases like multiple sclerosis and Type 1 diabetes; depression; heart disease; insulin resistance and Type 2 diabetes; and less-than-adequate immune functioning (translation: it’s harder to fight off that cold or flu). Increased awareness about Vitamin D, coupled with a 2011 report suggesting almost half of the U.S. population is deficient, has brought lots of attention to the vitamin and made it a top-selling dietary supplement.

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But conflicting health information has recently stirred confusion. How much Vitamin D do you really need? And what, if anything, are the benefits of Vitamin D? I’m breaking down the latest thoughts on the “sunshine vitamin” and sharing what we know, what we don’t know, and what this means for your health.

What Is Vitamin D Deficiency?

Turns out there’s no straightforward answer, largely because there’s disagreement on what Vitamin D levels “should” be. The Institute of Medicine (IOM), which sets the RDA, bases adequate Vitamin D levels as “generally adequate for bone and overall health in healthy individuals.” The Endocrine Society (ES) has set threshold levels slightly higher. However, while deficiency rates are debated, most do agree that a large portion of the population likely has Vitamin D levels lower than what is ideal. If you’re worried about being Vitamin D deficient, you can have a simple blood test done at your doctor’s office.

Vit D Levels*




< 12 ng/mL

< 20 ng/mL


12-20 ng/mL

21-29 ng/mL


≥ 20 ng/mL

≥ 30 ng/mL

*Using 25(OH)D blood values

How Much Vitamin D Do You Need Each Day?

Disagreement over how to assess healthy levels of Vitamin D means there are varying opinions over how much individuals need each day. The RDA for ages 1 to 70 years is 600 IU, an amount that is designed to maintain its definition of adequate levels. However, some research suggests a higher amount may be needed to reach and maintain its slightly higher definition of adequate levels. The ES clinical guidelines advise that 1500-2000 IU may be needed daily for adults over age 18 (ages 1-18 yrs, 600-1000 IU).

Should You Take Vitamin D Supplements?

Getting nutrients from food should be your first choice, and Vitamin D is found in egg yolks, fatty fish like salmon and sardines, and fortified dairy and grain products. But this limited list of sources can make it hard to meet the RDA—especially if you’re a vegetarian or vegan.

In the past, we thought short periods outside provided adequate sun exposure for the body to meet any remaining Vitamin D needs, but this doesn’t appear to be the case for many due to factors like geographical location, weather, pollution, sunscreen, and skin color. Vitamin D is a common supplement recommended by physicians to meet needs. Many recommend doses slightly higher than the RDA, but the optimal amount needed is not known and is likely highly individual. It is advised not to exceed 4,000 IU daily due to risk of adverse side effects.

Potential Benefits of Vitamin D

Bone Health

Consuming adequate Vitamin D (along with calcium) is key for bone health and prevention of osteoporosis, and the RDA is set to provide sufficient amounts for bone health. But some have speculated that more may be needed; others have questioned if consuming more than the RDA provides extra protection or can make up for past years of low intake. Based on a January 2019 study, high doses of Vitamin D (above recommendations) do not appear to reduce the risk of fractures or falls in the elderly or to provide any extra protection. What appears to be most key is getting enough Vitamin D on a daily basis. And if you weren’t diligent about getting Vitamin D and calcium in earlier years, your best bet is to start consuming adequate amounts now.

Cancer Prevention

Higher Vitamin D levels are associated with a decreased risk of colorectal cancer, and Vitamin D is thought to play a role in the prevention of certain cancers—specifically breast, colorectal, and prostate. However, the exact role that Vitamin D plays in each type of cancer is still being studied and is not well understood. It’s also not clear if low Vitamin D levels have an underlying role in cancer development, or if lower levels are a side effect. Some have suggested higher doses for cancer prevention, but the amount needed to possibly provide prevention, without harm, is unknown. Short-term studies suggest there is no change in cancer risk when higher dose Vitamin D supplements are taken. However, there are no studies looking at long-term consumption and impact on cancer risk.

Autoimmune Diseases

Lower levels of Vitamin D are associated with an increased risk of developing almost all autoimmune diseases, and the overall thought is that Vitamin D supplementation likely beneficial. Some research suggests that Vitamin D may reduce risk of developing Type 1 diabetes, but multiple sclerosis is where most research has focused. Individuals with higher Vitamin D levels have a lower risk of not only developing MS, but also a lower likelihood and severity of flareups in those diagnosed. Because of this, it’s suggested that Vitamin D supplements be part of the care plan for MS patients. More research is needed to determine what amount is “sufficient” to ease symptoms or to prevent MS. However, several initial studies have suggested that maintaining Vitamin D levels of 40ng/mL (above what both IOM and ES consider adequate) is the minimum to have an impact on MS.

Depression and Mental Health

A 2010 study using U.S. population data for almost 8,000 people found that those with lower levels of Vitamin D had significantly higher risks for depression. Other studies have had similar results, and also suggest a relationship between Vitamin D levels and depression severity. It’s clear that Vitamin D plays a role in both mental and cognitive brain functions. but researchers don’t know if insufficient Vitamin D levels play a role in causing depression or if lower vitamin D levels are a result of depression. To date, research has not indicated that Vitamin D supplements can improve symptoms or severity for those already suffering from depression.

The Bottom Line

It’s clear more research is needed to determine vitamin D’s role in immunity and disease prevention, so the best bet for most is to consume levels at or slightly above the RDA (with or without supplementation). Also, consider having your physician assess your Vitamin D lab values If you think you may be at risk.    

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