Vitamin D should be on everyone’s radar. People generally understand that vitamin D is important for boosting immunity, promoting healthy bone density and balancing calcium and phosphorus levels, but it does a whole lot more. Vitamin D supports brain health, muscle size and strength, heart health, mood, pancreas health and insulin balance.^1,2 Vitamin D is so important that a 2008 study found low blood levels are associated with double the risk of dying from any cause.³ Below are six surprising benefits of vitamin D and six more reasons to make sure you get enough of this powerful nutrient.

Cognition and Brain Health

Vitamin D can reach the brain by crossing the blood-brain barrier (BBB) through passive diffusion. Vitamin D exerts protects nerves and brain cells from damage by decreasing inflammatory chemicals and through its antioxidant properties.⁴ Vitamin D also stimulates the production of nerve growth factors (NGF).⁵ These growth factors promote the health and survival of nerves in various parts of the brain, including the hippocampus (memory region) and cortex (executive functions region). 

Additionally, vitamin D regulates the genetic expression of various neurotransmitters, including acetylcholine, dopamine, serotonin, and gamma amino-butyric acid (GABA).⁶

The benefits of vitamin D on brain function have been demonstrated in several clinical trials. In one, researchers tracked vitamin D status and cognitive function over 12 years in 1058 adults (median age 75 years old). They determined that people with vitamin D >30 nanograms per milliliter (ng/mL) had significantly better cognition, including memory and fluency, compared to those below that threshold. In fact, those with vitamin D >30 ng/mL performed at a level equivalent to being five years younger than those with lower vitamin D.⁷

While clinical trial results have been mixed, some have demonstrated the benefits of vitamin D on cognition. Taking as little as 800-1200 IU/day of vitamin D boosted cognition, with one study showing participants improved in as little as four weeks.^8,9

Muscle Strength

One of the most important predictors for dying is how large your thighs are. In an analysis of 19,885 patients, bigger thigh muscles (larger thigh circumference) was associated with an up to 21% lower risk of dying from any cause compared to people with smaller thighs. 

And it doesn’t take a lot to start benefitting from having more muscle. Every 1 cm (0.39 inches) increase in muscle size decreases your risk of dying from any cause by 3% and your risk of dying from heart disease by 5%.¹⁰ 

In addition to resistance exercise and eating enough protein, ensuring adequate vitamin D is important for muscle health. Vitamin D stimulates the production of cellular energy and proteins required for muscle contraction and relaxation. Research suggests that it also may directly stimulate muscle fiber growth, which is important for building and maintaining muscle mass and strength.^11-13 

Supporting these benefits was a randomized, placebo-controlled clinical trial of 21 mobility-limited women 65 years old or older who took either 4000 IU/day vitamin D3 or placebo for four months. When they started the clinical trial, they had a mean vitamin D blood level of 18.3 ng/mL. After four months of taking the dietary supplement, their blood vitamin D increased by 80% to a mean of 32.9 ng/mL. Additionally, in the women taking vitamin D3, their total muscle fibers increased by 10.6% compared to a 7.4% loss in muscle fibers in women taking the placebo.¹⁴ This study clearly demonstrated that supplementing with vitamin D3 promotes healthy muscle mass. 

Clinical trials have also shown that vitamin D3 improves muscle strength. In a review of 17 clinical trials with more than 5000 volunteers, researchers concluded that when someone’s vitamin D was less than 25 ng/mL, supplementing with vitamin D significantly boosted muscle strength.¹⁵ 

Falls and Fractures

Not only is vitamin D associated with more and stronger muscles, but higher levels of vitamin D are also associated with lower fall and fracture risks. In a review of five clinical trials with 1237 people, when their vitamin D levels were low (< 5 ng/mL) and then increased to > 40 ng/mL  by taking vitamin D with calcium, their risk for falling decreased by 22% compared to people taking a placebo or only taking calcium.¹⁶ 

At higher levels, vitamin D also maintains bone strength. Researchers concluded that blood vitamin D levels between 30 and 44 ng/mL (75-110 nmol/L) is associated with fewer falls and fracture. Vitamin D greater than 30 ng/mL is associated with a 20% decrease in nonvertebral fractures and an 18% decrease in hip fractures. Similarly, the greatest decrease in the risk for falling is seen when someone’s vitamin D was about 30 ng/mL and dying from any cause was reduced when the blood level was 40-48 ng/mL (100-120 nmoL/L).¹⁷

Healthy Mood

Lower levels of vitamin D have been associated with decreased mood and unhealthy levels of stress.¹⁸ While supplementing with vitamin D for promoting healthy mood has had mixed results in clinical trials, one intriguing study in women with PCOS showed that taking 50,000 IU of vitamin D every two weeks and a daily probiotic for 12 weeks promoted healthy mood compared to women taking placebo capsules.¹⁹ Unfortunately, this study design created some ambiguous results. We know that probiotics boost mood, so we can’t be sure if the benefits were from the probiotic, the vitamin D3 or the combination.

Another study, however, indicates that vitamin D3 by itself may be an important nutrient for promoting healthy mood. In a double-blind, randomized, placebo-controlled clinical trial, 42 people with major depression took either fluoxetine (Prozac, 20 mg/day) or fluoxetine plus 1500 IU/day vitamin D3 for eight weeks. At the end of the study, mood significantly improved in the people taking the vitamin D3 compared to those who only took the medication.²⁰ Another clinical trial also showed benefits with standard of care plus vitamin D3 in people with moderate depression.²¹

Modulating Inflammation

Inflammation is important for a healthy immune system. However, when there’s too much inflammation, or inflammation becomes chronic, it becomes toxic to cells and begins to damage them. In this way, promoting a healthy inflammatory balance is important. 

Inflammation is created by pro-inflammatory chemicals such as interleukin-1 (IL-1), IL-2, Il-6, tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma) and others. These are balanced by chemicals your body produces counteract these pro-inflammatory molecules and calms down the inflammation. These include IL-4 and IL-10. In animal studies, vitamin D has been shown to decrease the pro-inflammatory chemicals and increase those that counteract the inflammation and calm it down.²² 

The ability to balance inflammation has also been observed in humans. In a clinical trial, participants receiving vitamin D3 had significantly lower high-sensitivity c-reactive protein (hs-CRP) and significantly higher glutathione compared to placebo.¹⁹ CRP is increased when there’s inflammation, and glutathione is one of the body’s major antioxidants that scavenges free radicals and tamps down inflammation. 

An open label, randomized clinical trial of 50 volunteers who recently had heart attacks supports a mounting body evidence showing that vitamin D helps balance inflammation. Patients were randomized to receive 4000 IU/day of vitamin D3 or placebo. After only five days taking vitamin D3, the pro-inflammatory chemicals IL-6 and IL-8 significantly decreased while they increased in people not taking vitamin D3. Additionally, CRP was more than 300 times lower in people taking vitamin D compared to those taking the placebo, showing an overall beneficial effect of vitamin D3 on inflammation.²³

Pancreas and Insulin Health

Beta cells in the pancreas have the important job of manufacturing and secreting insulin when blood sugar get too high. In an important study, higher vitamin D has been associated with better insulin sensitivity and better beta cell function.²⁴ Not only have epidemiological studies found a link between low vitamin D levels and poor blood sugar control, a review of eight clinical trials with 4896 volunteers concluded that supplementing with vitamin D supports healthy blood sugar regulation.^25,26 Other researchers confirmed that vitamin D promotes healthy insulin, stimulates insulin secretion, promotes more and healthier beta cells and improves glucose uptake and insulin sensitivity.^22,27

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