What is Vitamin D and How Does It Impact Our Health?

Over the past several years, there have been some exciting advances in what we know and understand about vitamin D, including how it affects our overall health and well-being. And, while many people know that it has physical benefits for things like bone health, I have found that the maintenance of vitamin D levels is a critical component to mental health, as well.

In fact, it seems that without sufficient levels of vitamin D, it can be very difficult to address issues like depression, fatigue and muscle pain and weakness. Lately, studies have also linked vitamin D with other organ systems, forcing medical professionals to question whether or not they should more aggressively treat vitamin D deficiencies.

What is vitamin D?

Vitamin D is a fat-soluble vitamin that humans acquire naturally in three different ways:

  1. Exposure to sunlight. Scientifically speaking, sunlight on our skin converts cholesterol derivatives to vitamin D3, which is then processed in our liver to 25-hydroxyvitamin D3. In turn, that is converted by our kidney into an active form of vitamin D.
  2. Certain foods we eat. Mushrooms, yeast, egg yolks, fish (including wild-caught salmon, cod, tuna and sardines), milk and Swiss cheese are all great sources of vitamin D.  
  3. Our own livers. When necessary, our liver converts fat stores of vitamin D to its active form.

As time has gone on, we have seen an increased awareness about the dangers of excessive sun exposure due to skin cancer risks, and so most people rightfully apply more sunscreen when they go outdoors. However, one unexpected consequence of this behavior is that we wind up generating less vitamin D from our skin.

Because of this, we now must rely more on the foods we eat for our recommended daily value of vitamin D. Unfortunately, it is very difficult to get adequate levels through this method, even if we do regularly eat the foods lisdreamstime l 36021476 300x227 What is Vitamin D and How Does It Impact Our Health?ted above. That’s where vitamin D supplements are helpful.

Why is vitamin D so important?

Vitamin D has a myriad of benefits, and is critical for healthy bone metabolism and calcium regulations. There are vitamin D receptors all over the body, including in the brain and the digestive tract, and as a result it has an impact on mood, cognition, inflammation, the immune system, energy, blood sugar and our ability to manage cell division.

When we have low levels of the vitamin, it can have major negative effects on the body, including in our bone health where it is critical for bone mineralization. Without an adequate presence of vitamin D, a very small percentage of dietary calcium is absorbed into the bloodstream, meaning that the body is literally forced to start dissolving its own bone to maintain acceptable electrolyte levels. 

Chronically low levels of vitamin D can therefore cause osteoporosis and dramatically increases the risk of falls and broken bones. This is often fatal for the elderly.

In other areas of the body, preliminary studies suggest that there is a link between low vitamin D levels and issues like heart disease, diabetes, depression, multiple sclerosis, cancer, asthma and autoimmune disorders.  

Can we have too much vitamin D?

What complicates things is that it is very possible to have too much vitamin D in our system, which occurs when we take too many supplements (usually in excess of 10,000 IU per day). Ironically, decreased bone health has also been associated with having high levels of vitamin D in one’s system.

More specifically, blood levels higher than 60ng/mL of 25 hydroxyvitamin D have been linked with toxicity, pancreatic cancer and increased mortality. Simply put, while it is important to have a sufficient amount of vitamin D, it is possible to have too much of a good thing. The signs of vitamin D toxicity may include: 

  • Metallic taste and dry mouth
  • Headache
  • Dizziness
  • Nausea/Vomiting
  • Pancreatitis
  • Calcium build-up in the kidneys and blood vessels (nephrocalcinosis and vascular calcinosis)

To avoid vitamin D toxicity in people taking unsupervised over-the-counter vitamin D supplements, the Institute of Medicine (IOM) recently recommended a daily maximum of 4,000 IU per day for adults.

The Bottom Line

While individuals should be careful about how much they take, it is still important to note that taking vitamin D supplements might be a good option to prevent a wide range of potential health hazards. To learn more, I suggest speaking with your doctor about your vitamin D levels.

The Importance of Getting Tested for Low Vitamin D

While the impact of vitamin D on bone health and the immune system is fairly well-known, what many individuals do not realize is that low levels of the vitamin can have a negative impact on how well they recover from health issues like depression, bipolar disorder, muscle aches and fatigue.  In fact, low levels of vitamin D can be associated with low blood sugar levels and decreased energy, which may have a major effect on our everyday lives. With that in mind, it is important for people at risk of having low levels of vitamin D to have their levels checked by a physician. 

Certain people are more at risk than others, including the elderly, vegetarians, individuals with darker skin pigmentation and those who live in parts of the globe where there is limited exposure to sunlight. People who have conditions like inflammatory bowel disease, have had stomach surgery or are on certain anti-seizure medications or steroids may also have a heightened risk.

Low vitamin D levels may result in a variety of conditions, such as cardiovascular disease, diabetes, asthma, multiple sclerosis and cancer. There are also non-specific symptoms, including obesity, decreased cognitive function, back pain, muscle weakness, severe fatigue, depression, increased falls, tenderness in the chest or shin bones and muscles aches or throbbing in the hips, forearms and upper legs.

How are vitamin D levels measured?

The best indicator of your overall vitamin D status is your blood level of 25-hydroxyvitamin D, which reflects both dietary and sunlight-generated levels of the vitamin. However, it is important to note that these levels will vary depending on the season or how close to the equator you live, so if you are at risk for low levels of vitamin D, it is important to get tested often, preferably whenever the seasons change.

If tests do find that you have low levels, your doctor may recommend that you take vitamin D supplements. These supplements can help ensure that your body gets an adequate amount of the vitamin in order to function as effectively as possible.

If you feel that you may be at risk for low levels of vitamin D, I would encourage you to consult with your medical doctor soon. It just might change your life!


Bordelon P, Ghetu M, Langan R. Recognition and Management of Vitamin D Deficiency.  Am Fam Physcian. 2009;80(8):841-846.

DeLuca HF.  Overview of general physiologic features and functions of vitamin D. Am J Clin Nutr 2004; 80:Suppl: 16898-16968.

Ensrud K, et al “Circulating 25-hydroxyvitamin D levels and frailty status in older women”  J CLin Endocrinol Metab 2010;95:5266-5273.

Holick MF. Vitamin D deficiency.  N Engl J Med 2007; 357:266-81.

Institute of Medicine report on calcium and vitamin D.  Washington, DC:  Institute of Medicine 2010. 

Rosen CJ. Vitamin D Insufficiency. N Engl J Med 2011;364:248-254.

Rosen C, et al “Frailty: A D-ficiency Syndrome of Aging?” J Clin Endocrinol Metab 2010;95:5210-5212.

Schwalfenberg G. Not enough vitamin D: health consequences for Canadians. Can Family Physician.  2007;53(5): 841-854.

*The blog post on vitamin D does not address children below the age of 9, pregnant or lactating women. What is Vitamin D and How Does It Impact Our Health?

Learn more about vitamin D supplementation.

Comments are closed.