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Vitamin D Function & Benefits: Should You be Taking it?

Vitamin D Vitamin D
DaVinci Laboratories

Vitamin D is often referred to as the “sunshine” vitamin, as it is produced by the human body in response to sunlight exposure. Colloquially, it is said that we “get” vitamin D from the sun, but this is not quite accurate. Instead of being a vitamin obtained from diet and ingested, like most others, the human body actually synthesizes vitamin D in response to UV (ultraviolet) rays from the sun, specifically UVB.1 The processes that our cells undergo to synthesize vitamin D are complex and require modifications to the vitamin’s molecular structure. These modifications occur in the liver and then in the kidney, demonstrating how widely-used vitamin D is in the body.2

What is the Role of Vitamin D in Our Bodies?

Vitamin D is an essential vitamin for the body and plays a critical role in several key bodily functions. Let’s go over a few of the key ones.

Bone Health

One of the first functions that vitamin D was credited with was its ability to help cure rickets, a disease that is associated with weak and soft bones. Rickets can result when someone does not have enough vitamin D, and we now know that sufficient vitamin D is a major component in maintaining bone health.3 Vitamin D is used by the bones as a regulator to keep other crucial vitamins and minerals within a healthy range. Calcium and phosphorous are two substances that must precipitate into the bones to maintain strength and density. Vitamin D facilitates this precipitation, and assures that the body effectively absorbs other necessary vitamins and minerals for healthy bones.4

Cell Growth

As vitamin D is a fat-soluble vitamin, it is able to penetrate through the plasma membrane of the cell and bind with the genes within. This specific function allows vitamin D to play a role in cell growth and differentiation by affecting gene expression.5 Vitamin D has recently been shown to participate in the regulation of cell differentiation, apoptosis (programmed cell death), and even the production of tumorous cells. By deactivating proteins that prevent apoptosis, vitamin D can aid in slowing or stopping the proliferation of cancerous cells.6

Cardiovascular Health

The hormonal system of renin and angiotensin is a key player in the regulation of blood pressure and heart health. Overactivation of the system can be a cause for high blood pressure which can lead to stroke and heart attack. Sufficient levels of vitamin D in the body have been shown to suppress excessive activation of this hormonal system, thus keeping blood pressure in a normal range. This function of vitamin D is still under investigation, and its mechanism is not yet fully known, but multiple studies have shown a correlation between high vitamin D levels and decreased hypertension.7

Immune System

The immunological benefits of vitamin D have only become well-researched in recent years. Nevertheless, studies have shown that low levels of vitamin D in the body is correlated to higher rates of infection. As mentioned above, vitamin D plays a role in regulating cellular growth and proliferation. This is part of its function in the immune system specifically, as it can suppress proliferation of T and B cells which are key units of the innate immune system. Suppression is often seen as a negative effect, but in this case, vitamin D actually reduces the number of inflammatory immune cells in the body, and assures that these immune cells do not attack self.8

Mood Boosting

In recent years, associations have been made between vitamin D and mood disorders. Seasonal affective disorder (SAD) is one in particular that has been in focus as it occurs during the winter months where sunlight, a consequently vitamin D production, is down. A study comparing the effects of phototherapy versus vitamin D supplementation on individuals with SAD showed that vitamin D decreased feelings of depression associated with SAD more significantly than phototherapy. This suggests that it is not just lack of light, but our body’s inability to make a crucial vitamin due to a lack of sunlight, that causes seasonal depression.9

What Happens When We Are Deficient in Vitamin D?

Vitamin D deficiency is actually a very common problem around the world. This is partially due to changing lifestyles that require people to spend more time indoors. If your job requires you to be indoors all day, if you have darker skin, or if you wear high-coverage clothing, you are more likely to become vitamin D deficient. According to the International Journal of Health Sciences, more than 1 billion people on the planet are vitamin D deficient, qualifying it as an epidemic.10 Prevalence of serious diseases like multiple sclerosis, rheumatoid arthritis, or diabetes can be associated with long-term and severe vitamin D deficiency, but more mild cases can still result in higher infection risk and a depressed mood.8,9

How Can Vitamin D Deficiency Be Fixed?

The easiest answer to a vitamin D deficiency is getting more sunlight. You only need to be out in the sun for a short period of time each day, less than a half hour, in order to trigger production for sufficient vitamin D. It is easy to overdo sun exposure however, and you should still be conscientious of the other risks to your skin health that come with too much sun. For those who live in parts of the world with dark and cloudy winters, it might not be so easy to get sunlight exposure regularly. Also, some individuals who are taking certain medications that counteract with the sun, or small children, are advised to avoid the sun. In these and other cases, dietary supplementation of vitamin D may be necessary.11 There are many options for vitamin D supplements, ranging from sublinguals (like Frunutta), to gummies (like vitafusion gummy vitamins), to supplements especially geared toward children (like ChildLife Essentials). In addition to supplements, you can get vitamin D from some foods. Salmon, trout and fish oil contain vitamin D. Mushrooms are high in vitamin D, as well, along with fortified milks and cereals.2

So, as the weather warms up, don’t be afraid to spend a little time in the sun! Take a hike, go for a swim, or ride your bike around town. Of course, don’t forget your SPF if you plan on being out in the sun for long periods of time. Get outside and reap the benefits of vitamin D!


1 Nair R, & Maseeh A (2012). Vitamin D: The “sunshine” vitamin. Journal of Pharmacology & Pharmacotherapeutics. 3(2): 118-126.

2 National Institutes of Health (2020). Vitamin D Fact Sheet for Health Professionals. Retrieved from: https://ods.od.nih.gov/factsheets/VitaminD-health%20Professional/.

3 Pilz S, Zittermann A, Trummer C, Theiler-Schwetz V, Lerchbaum E, Keppel MH, Grübler MR, März W, & Pandis M. (2019). Vitamin D testing and treatment: a narrative review of current evidence. Endocrine Connections. 8(2): R27-R43.

4 Holick MF. (1996). Vitamin D and Bone Health. The Journal of Nutrition. 126(4): 1159S-1164S.

5 Samuel S & Sitrin MD. (2008). Vitamin D’s role in cell proliferation and differentiation. Nutrition Reviews. 66(2): S116-S124.

6 Umar M, Sastry KS, & Chouchane AI. (2018). Role of Vitamin D Beyond the Skeletal Function: A Review of the Molecular and Clinical Studies. International Journal of Molecular Sciences. 19(6): 1618.

7 Li YC, Kong J, Wei M, Chen Z, Liu SQ, & Cao L. (2002). 1,25-Dihydroxyvitamin D(3) Is a Negative Endocrine Regulator of the Renin-Angiotensin System. The Journal of Clinical Investigation. 110(2): 229-238.

8 Aranow C. (2011). Vitamin D and the Immune System. The Journal of Investigative Medicine. 59(6): 881-886.

9 Penckofer S, Kouba J, Byrn M, & Ferrans CE. (2010). Vitamin D and Depression: Where is all the Sunshine? Issues in Mental Health Nursing. 31(6): 385-393.

10 Naeem Z. (2010). Vitamin D Deficiency – An Ignored Epidemic. International Journal of Health Sciences. 4(1): V-VI.

11 Harvard Health Publishing (2019). Vitamin D and your health: Breaking old rules, raising new hopes. Retrieved from: www.health.harvard.edu/staying-healthy/vitamin-d-and-your-health-breaking-old-rules-raising-new-hopes.

Dr. Nicole Avena is a research neuroscientist and expert in the fields of nutrition, diet and addiction, with a special focus on nutrition during early life and pregnancy. Her research achievements have been honored by awards from several groups including the New York Academy of Sciences, the American Psychological Association, and the National Institute on Drug Abuse. She is an assistant professor of neuroscience at the Ichan School of Medicine at Mount Sinai, in New York, NY and is a visiting professor of health psychology at Princeton University in New Jersey. Dr. Avena has written several books, including What to Eat When You’re Pregnant and What to Feed Your Baby and Toddler. She regularly appears as a science expert on the Dr. Oz Show, Good Day NY and The Doctors, as well as many other news programs. Her work has been featured in Bloomberg Business Week, Time Magazine for Kids, The New York Times, Shape, Men’s Health, Details, as well as many other periodicals. Dr. Avena blogs for Psychology Today, is a member of the Penguin Random House Speakers Bureau and has the No. 2 most watched TED-ED Health talk, “How Sugar Affects Your Brain.” You can follow Dr. Avena on Twitter (@DrNicoleAvena), Facebook (www.facebook.com/DrNicoleAvena) and Instagram (@drnicoleavena), or visit www.drnicoleavena.com.