Vitamin D: Benefits and How Much You Really Need

Vitamin D, which is sometimes referred to as the “sunshine vitamin,” is produced in the skin in response to sunlight exposure. Although most commonly touted for its benefits of bone health, vitamin D impacts human health in many other ways as well.  

Vitamin D deficiency is becoming increasingly common as we spend more time indoors. Although the statistics on deficiency vary, researchers estimate that 40 to 50% of the world has deficient or inadequate vitamin D levels. 

Populations with an increased risk of vitamin D deficiency include older adults, obese individuals, people with darker skin, and people who live farther away from the equator where the sun doesn’t shine as strongly year-round. 

The most easily accessible source of vitamin D is sunshine, but there are a few foods that contain the vitamin: fatty fish, fortified milk, and mushrooms. Therefore, vitamin D supplements are a smart choice to achieve optimal levels, especially for those in the high-risk categories.

The Main Functions of Vitamin D

1. Bone and Muscle Strength

Vitamin D first came to be known for its bone-boosting benefits when it was found to cure rickets, which causes bowed legs and stunted growth. This is due to vitamin D’s ability to regulate phosphorus and calcium, which induces proper bone mineralization. 

Insufficient vitamin D can lead to loss of bone density, which is when the bones become brittle and can fracture. In a case-control study of postmenopausal women, each 10 ng/mL decrease in serum vitamin D levels was linked to a 33% increased risk of hip fracture. 

The active form of vitamin D binds to vitamin D receptors and can influence gene expression; these receptors have been found in almost all organs and tissues, including skeletal muscle. Vitamin D deficiency is associated with an increased risk of sarcopenia and muscle wasting with age. 

2. Improved Immune System Functioning

Vitamin D is involved in the regulation of the immune system in several ways. Vitamin D receptor expression is found in many immune cells; some immune cells take part in the conversion of inactive vitamin D into its active form. 

Vitamin D plays a role in both the innate and adaptive immune responses. The innate immune system provides the first line of defense against invading pathogens. Vitamin D helps this process by enhancing the production of the molecule cathelicidin antimicrobial peptide (CAMP), upregulating the production of other defensive immune cells, and strengthening the physical barrier function of epithelial cells. 

Additionally, vitamin D modulates the adaptive immune system through promoting the differentiation of naive T cells into protective regulatory T cells and reducing the secretion of pro-inflammatory cytokines. The immunomodulatory effects of vitamin D have been studied for its role in modulating autoimmune symptoms.

3. Improved Respiratory Health 

Related to its benefits to the immune system, vitamin D can reduce the risk of several respiratory illnesses, including tuberculosis, influenza, and upper respiratory tract infections. 

In a meta-analysis published in February 2017 in BMJ, people who took daily or weekly supplements of vitamin D had a 19% reduced risk of developing acute respiratory tract infections, with the strongest benefits seen in those who were vitamin D deficient.

Similar results were seen in a March 2010 trial published in the American Journal of Clinical Nutrition. School-aged children who received 1200 IU per day of vitamin D during flu season saw a significant reduction in the incidence of influenza, compared to children receiving a placebo.

4. Improved Mental Health

Studies have found that vitamin D deficiency is associated with an increased risk of depression, which is a leading cause of disease burden in developed countries. Depression is becoming increasingly common in older adults but tends to be under-diagnosed and under-treated. 

The therapeutic use of sunshine for depression or mood disorders has been used for decades; recent research has linked increases in vitamin D to this improvement. Similar results have been found using vitamin D or light therapy to treat seasonal affective disorder (SAD), which involves depression that arises in the sunless winter months.

A meta-analysis published in Nutrients in April 2014 found a significant improvement in depressive symptoms in those who took vitamin D supplements; the study noted improvements comparable to taking anti-depressant medication. 

5. Improved Heart Health

Vitamin D may support cardiovascular health through several different mechanisms. 

Vitamin D is able to inhibit cholesterol uptake and foam cell formation, which are inflammatory macrophages that increase fatty deposits on blood vessel walls and contribute to atherosclerosis. 

In addition, vitamin D improves cardiac health by inhibiting vascular calcification through ensuring calcium doesn’t build up around the heart. It can also regulate blood pressure, glucose metabolism, and improve insulin sensitivity, all of which are important cardiovascular health markers. 

In a large prospective study of over 41,000 individuals, vitamin D deficiency was significantly associated with coronary artery disease, heart failure, and having a stroke or heart attack.

6. Improved Gut Health

Vitamin D’s anti-inflammatory and immunomodulatory properties are a primary mechanism in how the vitamin positively impacts gut health. 

As mentioned earlier, vitamin D upregulates the production of antimicrobial peptides (CAMP) and improves the innate immune response in the gut. This helps to reduce dysbiosis and promotes healthy bacterial flora in the microbiome. 

Vitamin D deficiency is associated with an increased risk of inflammatory bowel diseases (IBD); the two forms of IBD are ulcerative colitis and Crohn’s disease, which affect different parts of the intestinal tract. 

Vitamin D has been linked to a reduced risk of developing IBD, as well as a reduction in the severity of the gastrointestinal symptoms that are characteristic of IBD.

People with IBD are also at increased risk of developing vitamin D deficiency, as the fat-soluble vitamin becomes difficult to absorb and utilize when the symptoms of IBD are flaring. Thus IBD patients may consider taking supplemental vitamin D. 

How Much Vitamin D Do We Need?

According to the National Institutes of Health, the recommended dietary allowance for vitamin D is 600 IU for adults up to age 70 and 800 IU for adults over age 70, with a serum vitamin D level of 20 ng/mL being considered adequate.

However, many researchers agree that these recommendations are set too low. The Endocrine Society recommends that adequate serum vitamin D levels should be above 30 ng/mL, which would require 1500-2000 IU per day for adults. Some functional medicine doctors recommend even higher serum vitamin D levels, ranging between 50 to 80 ng/mL.

Overall, supplemental vitamin D (in the form of D3) of 1000 to 4000 IU per day appears to be beneficial, with some research stating up to 8,000 IU per day for adults is safe for a shorter period of time in cases of deficiency. 

However, it’s important to know what your serum vitamin D levels are before you begin supplementing. Work with a healthcare practitioner to test your levels and find the correct vitamin D supplement dosage.

Key Takeaways

• Although the classical function of vitamin D is its effects on bone health, it also has anti-inflammatory and immunomodulatory properties.
• Vitamin D is linked to improved immune system functioning, reduced risk of respiratory diseases, and improvements in depression, heart health, and gut health. 
• The amount of vitamin D you need depends on your serum levels and risk factors, but 1000 to 4000 IUs per day appears to be suitable for most.

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