You may have heard that vitamin D builds strong bones, and that you can get vitamin D from the sun…but did you also know that vitamin D can reduce inflammation and is important for the functioning of cells, tissues, muscles, joints, bones, and more?  Today we’ll take a deeper dive into this versatile vitamin to learn what it does, why we need it, where to find it, and how to ensure we are getting enough.

What exactly is Vitamin D?

Vitamin D has been called the “sunshine vitamin” because we can synthesize it in the skin after exposure to UVB rays from the sun. A molecule in the skin, 7-DHC, is activated by the sun’s ultraviolet rays to “pre-vitamin D.” The pre-vitamin slowly transforms into vitamin D3, which is then transported to the liver, kidneys, and immune cells and is converted to its active form.

More recently, scientists have begun to classify vitamin D as a hormone as well as a vitamin; its structure is similar to that of estrogen, testosterone, and cortisone, and it acts to regulate calcium metabolism throughout the body.

What does it do?

Vitamin D levels play a significant role in a number of systems in the body, including immune and neurological regulation, and bone health. When levels of this nutrient are low, the risk of cancer, heart disease, autoimmune disorders, psychiatric disorders,  and mood problems increase.

Let’s take a look at a few of the specific actions and functions of Vitamin D in the body.

Moderates cell division: Vitamin D is a hormone whose function is to provide vital communication links between cells to normalize cell growth and prevent aggressive cell production. Vitamin D has shown promising activity in the fight against certain colorectal, breast, and prostate cancers through a few different mechanisms, some of which are not yet completely understood. Study authors concluded that vitamin D can be a useful addition to a cancer treatment protocol. They also suggest that vitamin D supplementation may prevent cancer development.

Promotes healthy immune system function. Recent studies have shown that vitamin D has modulatory effects on both the innate and adaptive immune system. In a fun little historical side note, before modern antibiotics, the treatment for tuberculosis patients at sanitoriums was sunlight and cod liver oil. Scientists now understand that both interventions increased vitamin D in the body. Vitamin D has since been shown to “stimulate the expression of anti-microbial peptides” in the immune system and lungs. It also prevents over-expression of inflammatory cytokines and increases expression of anti-inflammatory cytokines. On a macro level, vitamin D has been shown to reduce the incidence of respiratory infections in children and protect against ICU admission and death in COVID-19 patients 

Regulates calcium levels. The activated form of vitamin D3 has a few different actions to regulate calcium levels in the body.  When it binds to the vitamin D receptor in intestinal cells, the cells manufacture more calcium transporter proteins and binding proteins in the intestinal cells so the calcium passing through the intestine can get absorbed into the cell for utilization in the body.  Vitamin D also helps regulate calcium reabsorption from the kidneys, as well as into and out of bone.

Reduces inflammation in the brain and nervous system and improves depression. Vitamin D moderates the inflammatory processes in the neurological system. It has been reported that low vitamin D levels correlate with symptoms of depression, and that vitamin D supplementation may help improve negative emotions.

Promotes healthy glucose control. Vitamin D may be helpful in Type 2 diabetes, as it has been shown to increase insulin sensitivity by regulating insulin receptor expression. It may also directly stimulate the release of insulin from pancreatic cells. Vitamin D also has been shown to decrease risk for developing diabetes in people with pre-diabetes.

Why do you need it?

Deficiency of vitamin D has increased in the general population since people now spend more time indoors and use sunscreen when out. In children, vitamin D deficiency can lead to a condition known as “rickets,” which presents with bone pain, fractures, tooth deformity, muscle cramps, and skeletal deformities. In adults, a deficiency condition known as osteomalacia can cause bones to become soft and deformed.

Milder deficiency has been implicated in fatigue, depression, hair loss, muscle weakness, frequent colds or other illness, sleep disturbance, pale skin, lack of appetite, and bone pain. Deficiency is also associated with an increase in autoimmunity and autoimmune conditions.

As we age, our ability to produce vitamin D in the skin can decrease by as much as 50%. Overall vitamin D levels tend to decline, and our body’s ability to absorb calcium from the diet decreases. It can become more difficult for older adults to get all the vitamin D their body requires from diet and sunlight alone.

Where do you get it?

Since the 1930s, cow milk in the US was fortified with vitamin D to overcome the cases of rickets that were common among poor children in northern cities at that time. In recent years, many (but not all) plant-based milks are also fortified with vitamin D, as are some orange juice brands and many breakfast cereals. Vitamin D content is required to be reported on nutrition labels as of 2022. Vitamin D can be naturally found in egg yolks, fatty fish, cod liver oil, and beef liver.

As mentioned earlier, getting a healthy dose of sunshine can help increase vitamin D levels. The amount you can get will depend upon the time of year, location, amount of skin exposed, skin pigmentation, and duration of exposure. Studies suggest that the best time for optimal exposure with least risk is noon. One study in the UK  showed that 13 minutes of midday sunlight exposure three times per week during the summer was enough to maintain healthy vitamin D levels for Caucasian adults.

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