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Vitamin D

Also known as: Cholecalciferol (Vitamin D3), Ergocalciferol (Vitamin D2), 25-Dihydroxyvitamin D (Hormonally active yet not directly supplemented form), Calcitriol

Overview

Vitamin D is a fat-soluble nutrient. It is one of the 24 micronutrients critical for human survival. The sun is the major natural source, through eliciting vitamin D production in the skin, but vitamin D is also found naturally in oily fish and eggs and is often added to milk and milk alternatives.

Benefits

Vitamin D exerts its effects by binding to and activating the vitamin D receptor (VDR). Upon binding vitamin D, the VDR functions as a transcription factor, regulating the activity of over 1,000 different genes. This genomic action of vitamin D tends to be slower-acting, requiring the synthesis of new mRNA and proteins to take effect. Vitamin D also works through non-genomic mechanisms, causing rapid activation of various signaling pathways within the cell. Although VDRs have been identified on cell membranes, it isn’t currently known whether the more rapid, non-genomic action of vitamin D occurs through membrane-associated vitamin D receptors or a different cellular receptor. Although the most commonly associated effects of vitamin D on the body are associated with bone metabolism, the almost ubiquitous presence of VDRs in cells and tissues throughout the body indicates that vitamin D can affect a wide range of physiological processes. The additional effects of vitamin D on the body include, but aren’t limited to, the following: - Anticancer effects (promotion of cell death or suppressing proliferation in cancer cells) - Brain development - Cell differentiation - Anti-inflammatory effects - Antibacterial effects (through vitamin D’s effects on immune cells, and its promotion of the expression of genes encoding antimicrobial peptides) - Blood vessel protection - Nervous system health - Calcium regulation.

How it works

Supplemental vitamin D is associated with a range of benefits, including improved immune health, bone health, and well-being. Supplementation may also reduce the risk of cancer mortality, diabetes, and multiple sclerosis. Vitamin D is often taken for depression and similar mental health issues, but the evidence is mixed as to whether supplementation improves these outcomes. The effects of vitamin D likely depend on a person’s circulating levels of 25-hydroxyvitamin D (25(OH)D; a form of vitamin D that is measured in blood samples to determine vitamin D status), and many of the benefits of supplementation will only be seen when a deficiency is reversed.

Side effects

The ideal daily dose of vitamin D should correspond to its recommended daily allowance (RDA), which is currently 400–800 IU (10–20 μg) a day, but this may be too low for many adults. For moderate supplementation, a standard daily dose of 1,000–2,000 IU (25–50 μg) of vitamin D3 is sufficient to meet the needs of most people. Higher daily doses are in the range of 20–80 IU (0.5–2 μg) per kilogram of body weight. Vitamin D should be taken daily with meals or a source of fat. The recommended daily dose of vitamin D for pregnant women varies across different countries. In the US, pregnant women are recommended to take 600 IU (15 μg) of vitamin D daily, unless they have a vitamin D deficiency, which will require higher doses. In the UK, the recommended dosage is slightly lower, 400 IU (10 μg) daily.

Dosage

Very high vitamin D levels in the blood exceeding 375 nmol/L or 150 ng/mL are toxic, potentially causing side effects such as loss of appetite, nausea, vomiting, muscle weakness, confusion, dehydration, excessive thirst, and kidney stones. Extremely high blood levels of vitamin D can even be fatal. Since vitamin D production in the skin is self-limiting, sun exposure is unlikely to produce vitamin D levels that cause harm. However, vitamin D levels in the blood can readily reach toxic levels with chronic, high-level supplementation. Although ultra-high-level supplementation is universally considered to be toxic, there’s some debate on what constitutes the upper limit for safe, moderate-level supplementation. Taking around 4,000 IU (100 μg) of vitamin D per day for extended periods (≥6 months) seems to increase the risk of hypercalcemia (high blood calcium) and, among older adults, the likelihood of experiencing a fall.

FAQs

What is vitamin D?

Is there a difference between Vitamin D2 and Vitamin D3?

There are two forms of Vitamin D found in food and supplements: Vitamin D2, which is found in mushrooms, and Vitamin D3, which is found in animal foods. Vitamin D2 is not as bioavailable as D3, which means your body cannot use it as readily; however, it can still raise your vitamin D levels.

What are some dietary sources of vitamin D3?

Dietary sources of vitamin D include the following foods: fatty fish (such as tuna or salmon), fish liver oil, beef liver, egg yolks.

What are vitamin D’s main benefits?

Can vitamin D status affect testosterone levels?

Potentially. Vitamin D status was associated with androgen levels in men in an observational study, and a randomized controlled trial found that Vitamin D supplementation (around 3000 IU/day or 75 μg/day) increased testosterone levels in healthy overweight men.

Is there a link between vitamin D levels and all-cause mortality?

Low vitamin D levels may be linked to increased all-cause mortality, particularly in older adults. Observational studies have shown a general trend for associations between low vitamin D levels and all-cause mortality in general and elderly populations.

Can vitamin D supplementation improve symptoms of multiple sclerosis?

Multiple sclerosis (MS) is an autoimmune disease that affects the myelin sheath of neurons. There are associations between residing in latitudes further away from the equator and increased risk of MS, and more sun exposure during childhood is associated with reduced risk of MS during adulthood.

Can vitamin D supplementation help with treatment or prevention of Alzheimer’s disease?

Numerous studies have been published suggesting that vitamin D may help to ameliorate some factors associated with the etiology of Alzheimer’s disease.

Can vitamin D supplementation help with the treatment or prevention of other neurodegenerative diseases?

Preclinical studies on vitamin D have indicated that it may interact with and interfere with various signaling pathways associated with other neurodegenerative diseases, such as Parkinson’s disease, multiple sclerosis, and vascular dementia.

Can vitamin D help with erectile dysfunction?

Research suggests that there may be a link between low vitamin D levels and the risk of developing erectile dysfunction (ED), but there is not yet a known dose for treating it.

Can vitamin D alleviate depression?

Many people get depressed during the winter months, when we produce less vitamin D. Vitamin D is the sunshine vitamin, and sunshine is implicated in mood. However, depression is complex, and the mechanisms at work are not well-understood.

What are vitamin D’s main drawbacks?

Do vitamin D supplements interact with any medications?

Vitamin D supplements have the potential for interactions with certain medications. It is important to discuss vitamin D supplementation with your healthcare provider when taking any prescription medications.