Our bodies primarily use vitamin D to absorb calcium in order to build and maintain healthy bones. However, this crucial nutrient also regulates many other important systems and functions. "Its anti-inflammatory, antioxidant and neuroprotective properties support immune health, muscle function, and brain cell activity," Mayo Clinic points out.
Chris Mohr, PhD, RD, fitness and nutrition advisor at Barbend, says that’s why there are plenty of potential benefits associated with taking vitamin D supplements, in addition to raising your levels naturally through sun exposure and vitamin D-rich foods. In particular, supplements may help to fend off illness, improve mood and mental health, stabilize blood sugar, reduce blood pressure, enhance heart health, and maintain a healthy weight.
However, vitamin D can also cause side effects affecting several body systems—especially when taken in high doses over the safe upper limit of 4,000 IU per day. Read on to learn the eight surprising vitamin D side effects to look out for, according to medical experts. Then, be sure to discuss with your doctor whether you’re getting the right amount.
RELATED: 16 Vitamin D Deficiency Symptoms to Watch Out For, According to Doctors.
1. Nausea or digestive issues
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According to Raj Dasgupta, MD, chief medical advisor for Garage Gym Reviews, one of the most common side effects of taking vitamin D is that it can lead to upset stomach, nausea, vomiting, or even constipation.
"This happens because vitamin D boosts calcium absorption, and too much calcium in your bloodstream (called hypercalcemia) can irritate your digestive system," he explains.
"If you’re noticing these symptoms, it’s worth checking in with your doctor and possibly scaling back your dose. Vitamin D toxicity is rare, but it can be dangerous," Dasgupta warns.
2. Kidney stones
iStockTaking Vitamin D supplements can help to increase calcium levels in the blood by increasing the amount of calcium absorbed from the intestines. While this can be a good thing for those whose calcium levels are low, it can have an unintended consequence for some: kidney stones.
"While vitamin D is great for your bones, too much of it can raise calcium levels so high that it starts forming kidney stones," says Dasgupta. "This is especially a concern for people who are already prone to stones."
"Staying hydrated and sticking to recommended doses can help keep this from becoming a problem," he notes.
RELATED: 6 Signs You’re Getting Too Much Calcium, According to Doctors.
3. Dehydration, excessive thirst, and frequent urination
ShutterstockMohr says that excessive vitamin D can also lead to dehydration because it increases calcium absorption, which can raise calcium levels in the blood.
"This can trigger symptoms like excessive thirst and frequent urination as your body tries to get rid of the extra calcium. Staying hydrated and monitoring vitamin D intake can help avoid this issue, as vitamin D is a fat-soluble vitamin that is stored in the body, rather than excreted like some others," he explains.
4. Mood swings or irritability
iStockGetting more vitamin D—especially from natural sun exposure—can help to boost your mood and stave off depressive symptoms. However, some who take vitamin D in large doses may find that they experience mood swings or heightened irritability.
"Although vitamin D is often linked to better moods, taking too much can have the opposite effect," says Dasgupta. "High calcium levels caused by excess vitamin D can dysregulate the balance of brain chemicals, leaving some people feeling irritable, anxious, or even down."
"If your mood changes after starting a supplement, it might be time to reevaluate your dose," he advises.
RELATED: 5 Supplements That Can Damage Your Kidneys, Doctors Say.
5. Poor appetite and weight Loss
iStockIf you take vitamin D and have noticed changes to your weight or appetite, Mohr says it’s a good idea to discuss this with your doctor.
"High levels of vitamin D may lower your appetite and cause unintentional weight loss due to hypercalcemia. Elevated calcium levels can disrupt the digestive system and lead to symptoms like nausea or abdominal discomfort," Mohr explains, noting that these can curb one’s appetite.
6. Bone pain or bone weakness
ShutterstockVitamin D is often used to help prevent or treat osteoporosis in older adults. However, excessively high doses can actually degrade your bone health over time.
"It might sound odd, but overloading on vitamin D can actually weaken your bones," Dasgupta says. “High doses of vitamin D can increase the production of osteoclasts, which break down bone. This can result in excessive calcium in the blood from your body pulling minerals out of your bones, making them more brittle."
RELATED: 12 Supplements You Should Never Take Together, Medical Experts Say.
7. Heart palpitations or irregular heartbeat
iStockHaving a vitamin D deficiency can cause heart palpitations or irregular heartbeat—but so can high calcium levels. This can occur as a result of taking too much vitamin D.
"Calcium plays a role in how your heart beats, so too much can throw things off. If you notice your heart racing after starting vitamin D, it’s a good idea to talk to your doctor right away," advises Dasgupta.
8. Fatigue and weakness
ShutterstockVitamin D plays a role in regulating dopamine and serotonin, which is why having a vitamin D deficiency can contribute to a feeling of fatigue or weakness.
"However, having too much vitamin D can actually make you feel tired or weak, too," notes Mohr. This is likely due to biochemical imbalances caused by high calcium levels. This can affect muscles and overall energy levels, making it harder to stay active."
If you’re taking vitamin D and have noticed any side effects, be sure to discuss them with your healthcare provider. "It is always important to have your blood levels of vitamin D tested before blindly supplementing with additional vitamins. More isn't always better," Mohr says.
