Vitamin D has long been touted for its ability to strengthen bones and improve mood, but researchers continue to discover unexpected links between this essential nutrient and our bodies.

Vitamin D can be found in food sources such as fatty fish, fish liver oil and egg yolk, as well as being available as a dietary supplement. Many governmental and medical societies have established guidelines for measuring vitamin D sufficiency levels.

1. Bone Health

Vitamin D helps the body absorb calcium, strengthening bones. Children lacking enough Vitamin D develop rickets – an illness in which bones weaken and deformities such as bow legs occur – while in adults vitamin D deficiency may result in osteoporosis, the gradual loss of bone density that increases fracture risk over time.

The National Academy of Sciences, Engineering and Medicine defines vitamin D deficiency as serum 25(OH)D concentrations below 30 ng/ml, while people with higher serum 25(OH)D levels between 30-50 ng/ml are considered adequate in their vitamin D consumption. According to IOM recommendations, individuals should seek adequate intakes of vitamin D in order to ensure bone health as well as reduce chronic diseases such as cancer, cardiovascular disease diabetes and inflammatory disorders.

Recent findings of a widely reported study investigating the effect of Vitamin D dietary supplements on bone health were shocking to many medical researchers, casting doubt upon widespread belief that older men and women need high doses of Vitamin D to protect themselves against future fractures as they age. The New England Journal of Medicine published its study’s results, which led them to question this widely held belief and cast doubt upon long-held belief that taking large amounts of Vitamin D to avoid fractures was the key way forward.

VITAL study results demonstrate that daily supplementation of 400, 4000, or 10 000 IU of Vitamin D for three years did not significantly alter total or cortical trabecular BMD or fracture risk in healthy community-dwelling adults with adequate calcium intake; results were similar for both primary and secondary analysis while accounting for any potential confounders.

The authors believe that vitamin D supplementation’s lack of an impactful response on bone health was due to its immunoregulatory properties and interaction with cytokine concentration levels. Researchers point out that their findings do not indicate that IOM committee’s advice of adequate vitamin D consumption is unwarranted, since the evidence supports other benefits associated with adequate levels of Vitamin D status. As examples of potential outcomes from Vitamin D supplementation, researchers point out a decrease in respiratory infections, autoimmune diseases and cardiovascular diseases. They suggest that future Mendelian randomization studies involving Vitamin D should utilize optimized instrumentation in densely phenotyped biobanks that will facilitate causal effect estimation.

2. Immune System

Vitamin D has long been revered for its important physiological roles in calcium absorption and bone health; it’s also an invaluable immunomodulator, aiding normal immune homeostasis. Your skin produces vitamin D in two forms (25(OH)D and 1,25(OH)2D), while certain plants, animals, fungi, and microbes also produce it when exposed to sunlight (12). You can find vitamin D-rich foods like oily fish, fortified milks yoghurts and cereals, while supplements are also available – in either case!

Vitamin D binding to its receptor in cells can result in its transformation into the active steroid hormone calcitriol, with multiple major biological effects. For instance, it enhances innate immunity by activating cathelicidins and defensins to produce antimicrobial peptides that destroy invading bacteria or viruses by disintegrating their cell membranes; additionally calcitriol activates macrophages and monocytes for further defense against microorganisms.

Researchers have also discovered that vitamin D helps our immune system detect and respond rapidly and effectively against invading viruses or bacteria, providing us with the opportunity to mount rapid and effective defenses against pathogens. It does this by “trigger”ing our killer T cells into action – turning inactive immune cells into ones ‘primed’ to seek out and destroy any remaining signs of the pathogen or virus.

Studies have demonstrated that individuals with low serum vitamin D levels are more prone to contracting SARS-CoV-2 infection. A large study conducted on this matter demonstrated this fact; those with vitamin D serum levels below 20 ng/mL had a 54% higher positivity rate for SARS-CoV-2 than those with levels 55 ng/mL or above; these results have spurred research on whether supplementing vitamin D safely and affordably could provide an adaptive immune response against infectious diseases like SARS-CoV-2; several other studies have linked vitamin D with reduced risk in terms of conditions like rheumatoid arthritis, diabetes and autoimmunity(13, 14).

3. Cardiovascular Health

Vitamin D’s beneficial impact on heart health extends far beyond just managing blood pressure and inflammation. The micronutrient also aids blood vessel health by supporting circulation that prevents plaque build-up – one reason many studies have linked low levels of vitamin D with cardiovascular disease, especially among older adults.

Studies conducted using observational approaches have demonstrated a correlation between high blood levels of vitamin D and lower rates of major cardiovascular events such as stroke, myocardial infarction or coronary revascularisation; but correlation does not prove causation and randomized clinical trials must be performed to validate whether its benefits exist in reality.

The VITAL trial, published in the New England Journal of Medicine, examined whether supplementing with vitamin D significantly decreased major adverse cardiovascular events (MACE). Unfortunately, no evidence was found to support that view; instead it indicated no significant reduction of MACE by using daily dosing of 2,000 IUs rather than weekly dosing for five years in either group of participants. MACE rates did not vary by sex or concurrent calcium administration or pretreatment 25-hydroxyvitamin D levels (25 ng/mL vs higher), BMI or age groups either.

However, MACE rates were much lower among a subgroup of people taking statins or cardiovascular medications prior to participating in this study, suggesting this might explain why MACE reduction wasn’t seen across all study participants.

Researchers are exploring other factors that might have had an effect on this study’s outcomes, including genetic links that might cause differences in how our bodies use and metabolize vitamin D, environmental influences such as diet and lifestyle, vitamin D requirements and bioavailability, health outcomes, as well as personalized vitamin D recommendations. A blood vitamin D test can give an idea of how much is required based on personal circumstances – testing your levels regularly will give a good indication as to if you’re getting adequate amounts.

4. Mental Health

Studies have indicated that low vitamin D levels are linked to depression and anxiety. Both of these mood disorders affect quality of life as well as increase disease burden, so finding ways to prevent or treat them is paramount; one effective strategy to do this may include increasing vitamin D consumption.

As suggested by two meta-analyses ([15] and ), vitamin D could help alleviate symptoms by correcting hormonal imbalance, while also helping counter oxidative stress and inflammation; an antioxidative property of vitamin D might further alleviate depression symptoms. For anxiety disorders, one possible mechanism might be that vitamin D helps regulate serotonin and melatonin neurotransmitters that have an impact on sleep and mood regulation (serotonergic) neurotransmitters that contribute to their effects.

Vitamin D can easily cross the blood-brain barrier and enter neurons, where its presence has been demonstrated to have an beneficial impact on memory and learning functions. Furthermore, it plays a crucial role in maintaining balance among signals that stimulate or inhibit brain activity – an intricate system thought to be compromised in disorders like autism and schizophrenia.

However, most observational studies have yielded mixed results regarding whether vitamin D supplementation improves mood. This could be because someone’s vitamin D status could simply reflect another influencer such as diet or genetic makeup; thus randomized clinical trials that match people taking vitamin D with comparable controls are required to provide definitive answers on this matter.

Okereke and his team recently conducted a study using data from VITAL, one of the world’s largest randomized vitamin D trials ever to date, to examine how vitamin D might impact depression. While overall results were inconclusive, his team discovered that in certain subgroups of participants it significantly reduced risk. This opens up possibilities for future research to optimize supplementation for mood; alternatively combining it with traditional treatments for depression such as psychotherapy or antidepressants could prove effective as well.