Vitamin D3, also known as cholecalciferol, helps your body absorb calcium. Having normal vitamin D, calcium, and phosphate levels is essential for building and maintaining strong bones. Conversely, vitamin D deficiency is linked to osteoporosis, reduced bone density, fragility, and increased risk of falls.

Vitamin D3 also plays a role in immune function and protection against cell damage. Vitamin D deficiency has been linked to an increased risk of common cancers, autoimmune disorders, high blood pressure, and infectious diseases.

Any injectable medication requires a prescription for use, including vitamin D3 injections.

Vitamin D is a fat-soluble vitamin that is stored in the body. Side effects from excess vitamin D are typically due to increased calcium levels.  Potential side effects of vitamin D supplements include:

• Muscle weakness
• Bone pain
• Extreme thirst
• Kidney stones
• Frequent urination
• Decreased appetite
• Fatigue
• Confusion
• Pain at the injection site
• Nausea
• Headache
• Constipation
• Irregular, fast, or slow heartbeat

Foods highest in vitamin D are:

• Cod liver oil
• Rainbow trout
• Salmon
• White mushrooms
• Vitamin D fortified cow’s milk
• Vitamin D fortified soy milk
• Vitamin D fortified cereals
• Sardines
• Eggs

Vitamin D deficiency is common. According to the NIH, most people in the U.S. consume less than the recommended amounts of vitamin D.

Groups at highest risk for vitamin D deficiency:

• Older adults
• People who limit their sun exposure or live further from the equator
• People with darker pigmented skin
• People who are overweight or obese
• People with medical conditions that limit fat absorption

Although vitamin D does not darken skin, there is a link between skin pigmentation and vitamin D levels. Melanin, the pigment that darkens the skin, increases due to UV light exposure. It shields the DNA of epidermal cells from UV rays. Damaged DNA increases the possibility of mutations that lead to skin cancer.

In contrast, too much melanin can interfere with vitamin D production in the skin. Darker pigmented skin was an evolutionary advantage early in human history when everyone lived near the equator because it protected against skin cancer. More melanin was a tradeoff for less vitamin D as people migrated north and south.

According to some studies, there is a direct relationship between skin pigmentation and the skin’s ability to produce vitamin D3. However, others do not reach the same conclusion, suggesting that genetic factors, baseline vitamin D levels, and the duration and dose of UV light influence vitamin D production in the skin.

In December, January, and February, there is almost no vitamin D effective UV radiation at 40 degrees latitude.

At 90 degrees latitude, there is no effective vitamin D radiation for eight months out of the year.

Anyone who lives above the 35th parallel, which runs through the middle of the United States, will not get enough vitamin D during the winter because the sun’s angle with the earth is too great.

Even in the summer, you may be at risk for vitamin D deficiency because, according to a recent survey, Americans spend only 7.6 percent of their time outside.

Vitamin D deficiency is more common in people who are overweight or have obesity. Vitamin D is a fat-soluble vitamin. Increased body fat means more storage for vitamin D. The body needs access to soluble vitamin D.

A study comparing participants at a  normal weight to obese and overweight subjects found they had a serum vitamin D level that was 7.9 ng/ml lower and 3.2 ng/ml lower, respectively. It appears that belly fat has the biggest impact on vitamin D levels.

Other confounding variables may be that people who are obese may be less able to move around and get outside and may have an increased incidence of bariatric surgery, leading to malabsorption of fat-soluble vitamins.

The endocrine societies recommend that individuals with obesity be given 2 to 3 times more vitamin D supplementation to correct a deficiency than those of average weight.

There is accumulating evidence suggesting a relationship between vitamin D and obesity. More research is needed to fully understand what the relationship is.