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7 Things to Know About Vitamin D

What to know about vitamin D, according to experts.
FACT CHECKED BY Emilia Paluszek

Vitamin D is a vital nutrient that helps our body absorb calcium and phosphorus, which are essential in building strong bones. In addition, Harvard Health states, "Laboratory studies show that vitamin D can reduce cancer cell growth, help control infections and reduce inflammation. Many of the body's organs and tissues have receptors for vitamin D, which suggest important roles beyond bone health, and scientists are actively investigating other possible functions." That said, getting enough vitamin D can be a challenge for some because few foods naturally contain the nutrient and working from home or an office can limit one's time to go outside and grab some sunshine, which is another way to get vitamin D. Supplements are another option and Eat This, Not That! Health spoke with Dr. Jeffrey Dlott, Senior Medical Director of QuestDirect who explained what to know about vitamin D before taking it. As always please consult with your physician for medical advice. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Almost Half of Americans are Deficient in Vitamin D

Shot of a doctor explaining a medical procedure with a model to a senior patient while sitting in her office

Dr. Dlott says, "Approximately 40 percent of Americans are vitamin D deficient, and a deficiency can have adverse health effects over time. In children, vitamin D deficiency can cause rickets – which is rare, and in adults it can cause softening of bones, a condition known as osteomalacia, resulting in poor bone density and weakness in muscles. A long-term deficiency can also lead to osteoporosis."


Certain Health Issues Can Increase the Chance of a Vitamin D Deficiency

Female orthopedist massaging middle-aged woman in clinic.

According to Dr. Dlott, "Certain medical conditions can also increase your risk of deficiency, including celiac disease, Crohn's disease, obesity, or kidney and liver disease, and age can also be a factor; as we get older, our skin's ability to make vitamin D decreases." 


COVID's Link to Vitamin D Deficiency

Young sick woman laying in her bed.

Dr. Dlott explains, "One of the most important functions of vitamin D in the body is that it helps the body absorb calcium, so it's important to get enough vitamin D to help build and maintain healthy bones. Vitamin D also helps support immune health, muscle function and brain cell activity. There is also research to suggest that vitamin D may help reduce the chance of heart disease, and inadequate levels may increase the risk of infections and autoimmune disease including rheumatoid arthritis, type 1 diabetes, and inflammatory bowel disease. Recent studies have also explored the link between COVID-19 and vitamin D, and while links are not necessarily considered to be causal, one such study found that 80 percent of people diagnosed with COVID-19 had deficient levels of vitamin D. "


Ways to Get Vitamin D and How to Tell If You're Deficient

happy woman stretching arms in sunshine

"Sunlight and certain foods allow you to get vitamin D into your body, and supplements are another source if you aren't getting adequate levels through sunlight exposure and diet," says Dr. Dlott. Vitamin D doesn't occur naturally in a large variety of foods, and most vitamin D sources in the American diet come from vitamin D-fortified foods. For example, nearly all dairy milk sold in the US is fortified with vitamin D, as are most yogurts, plant-based milks, and orange juice. Fatty fish, like salmon, tuna and trout, are the best natural sources, and some animal products including eggs and cheese have lower levels of vitamin D. The amount of vitamin D your skin makes through sun exposure also depends on a variety of factors, including the season, where you live in relation to the equator – the further you live from the equator, the less exposure you may have, and the pigment of your skin. Those with darker complexions have a reduced ability to make vitamin D from sun exposure. Supplements can help people achieve optimal vitamin D levels if other sources are not enough, but it's always a good idea to check in with a doctor before starting any new supplement. In the case of vitamin D, it is possible to consume too much and that can potentially lead to other health issues. A doctor can determine if you have a vitamin D deficiency or if you're at risk of one through a blood test. There are also test options available that consumers can purchase themselves."


You Can Overdose on Vitamin D


Dr. Dlott shares, "While it is not common, people can experience vitamin D toxicity as a result of accidental overdose, prescription errors, or misuse of high-dose vitamin D supplements. There is a bit of variance in recommended vitamin D levels, but levels between 30-60 nanograms (ng) per mL is generally considered optimal. Experts recommend that people with typical vitamin D levels take no more than 4,000 IU of vitamin D per day. Vitamin D toxicity can lead to elevated blood calcium levels, with symptoms including vomiting, nausea, fatigue, dizziness, loss of appetite, kidney stones, and high blood pressure, or elevated blood vitamin D levels. Again, it is rare, but it's important that people have oversight from a healthcare provider when taking any supplements." 


Signs of a Vitamin D Deficiency to Watch Out For

man getting blood test

Dr. Dlott explains, "People with a vitamin D deficiency may experience symptoms including muscle weakness, pain, fatigue, and depression. However, some people may not present with symptoms. It can also be difficult to determine if symptoms are linked to a vitamin D deficiency or another issue, so it's important to get a blood test to determine if it is a vitamin deficiency or something else."


Always Speak to Your Physician Before Taking Supplements

Female doctor talking while explaining medical treatment to patient through a video call with laptop in the consultation.

Speaking with a healthcare provider is important before adding any vitamins or supplements to your diet for a number of reasons," Dr. Dlott says. "For one, there is potential for drug interactions with other medications you are taking, and certain supplements may exacerbate health issues. A doctor can also provide guidance to help find supplements that are safe to take and answer any questions about nutritional supplements. In some cases, you can take too much of a good thing. In the case of vitamin D along with vitamins A, E, and K, taking more than is needed can have adverse health effects, so it's important that you're not taking unnecessary supplements. Dietary supplements are also classified as a category of food rather than a drug or medicine, and they are not regulated by the Food and Drug Administration (FDA). This means that the FDA is not authorized to evaluate a supplement for safety and effectiveness or if marketing claims live up to how a supplement is positioned.  Sharing information about any vitamins or supplements you are taking with your healthcare provider also provides a full picture of your overall health, which is important to ensure that your doctor can help make informed healthcare decisions and improve the quality of the care you're receiving." 

Heather Newgen
Heather Newgen has two decades of experience reporting and writing about health, fitness, entertainment and travel. Heather currently freelances for several publications. Read more about Heather