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Surprising Side Effects of Taking Vitamin D Supplements, Says Science

What can happen to your body when you take this immune-boosting supplement.
FACT CHECKED BY Olivia Tarantino

Vitamin D has become an increasingly popular supplement for adults, especially considering deficiencies of this vitamin are not uncommon, that the vitamin is linked to immune support, and that current research supports plenty of health benefits associated with appropriate intake of vitamin D.

While your body can produce this vitamin with exposure to the sun, most adults should rely on consuming vitamin D through food and supplement as well to ensure adequate intake. Vitamin D supplementation may provide an extensive list of health benefits; however, it is important to speak with your physician about your supplementation protocol as blood levels of vitamin D can easily rise to a dangerous level that may negatively impact your health.

Here are some side effects you may notice when taking vitamin D supplement. Read on, and for more on how to eat healthy, don't miss 7 Healthiest Foods to Eat Right Now.

Mental health perks.

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While this is an area of vitamin D research that needs more depth and time, recent studies indicate there may be a link between vitamin D and depression. In fact, a Neuropsychiatry review found a relationship between increased incidence of depression and vitamin D deficiency. (Read on: 5 Signs of Vitamin D Deficiency You Should Never Ignore.)

Immune system support.


You know the common nutrients associated with immunity, like vitamin C and antioxidants, but there is also research to support vitamin D may play a role in creating a healthy immune system. A 2017 study indicated supplementation of vitamin D may reduce the risk of acute respiratory tract infection, especially in subjects who started the study with a more significant deficiency of vitamin D. Additionally, a separate review found vitamin D deficiency may increase susceptibility to infection.

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Lower blood pressure.

Vitamin D

According to the Center for Disease Control and Prevention, nearly half of adults in the United States have high blood pressure, otherwise known as hypertension. While we know maintaining a healthy weight, regular exercise, and managing dietary sodium are ways to improve blood pressure, research indicates vitamin D may play a role as well.

A 2019 study highlights that a vitamin D deficiency is associated with an increased risk of cardiovascular disease related to hypertension, and even brief bouts of deficiency may raise blood pressure enough to negatively impact organ health. While lifestyle and dietary choices can be made to manage blood pressure, this research suggests vitamin D supplementation may be beneficial as well.

Elevated blood calcium levels.


While there are clear benefits to supplementing with vitamin D, especially for those who have a deficiency, it is possible to overdo it and reach toxic levels. One thing that can happen if you over supplement with vitamin D is that you may over absorb calcium.

An important role of vitamin D is to help your body absorb calcium, hence the bone-health function of vitamin D you have likely heard before. However, if taken in excess, vitamin D may instruct your body to over absorb calcium, and in turn, result in hypercalcemia, or high blood calcium levels. With symptoms like nausea and vomiting, weakness, confusion, and muscle pain, hypercalcemia may not sound detrimental, however, research has found it can take months to reduce calcium level back to normal following periods of high blood calcium levels. On the other hand, without sufficient vitamin D, you may be interested to know about the One Major Side Effect of Not Eating Enough Calcium, New Study Says.

Loss of bone.

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This may seem counterintuitive as we just reenforced the bone-building benefits of vitamin D; however, research suggests that excessive intake of vitamin D may lead to low levels of vitamin K, another vitamin with an important role in bone health. Vitamin K aids in the regulation of osteocalcin, a hormone that plays a role in the calcification of bone, enabling bones to build strength and rigidity. With lowered levels of vitamin K within the body due to excessive intake of vitamin D, bone health may be negatively impacted. To offset this, ensure you are taking appropriate amounts of vitamin D and enjoy vitamin K-rich foods like kale and spinach.

Kidney injury.

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Your kidneys are responsible for filtering your blood. So, after your body digests supplements, it goes through your kidney to then be dispersed throughout the body. What often can happen when you consume too much of a supplement, the kidneys can get overrun and possibly damaged.

Research has shown consistently that vitamin D toxicity, and consequent hypercalcemia, can result in kidney dysfunction and possible failure. Additionally, this outcome has been seen in individuals with existing kidney disease as well as those with healthy kidneys. While kidney failure can be treated with hydration and medication, this is a serious outcome with the potential to lead to serious and long-lasting effects within the body.

For more, check out Popular Foods That May Cause Lasting Damage to Your Kidneys, Says Science.

Melissa Rifkin, MS, RDN, CDN
Melissa is a Connecticut-based registered dietitian with over 15 years of experience, including clinical and outpatient settings, and runs the popular nutrition education Instagram account, Confessionofadietitian. Read more about Melissa