Vitamin D Side Effects: What To Know About Taking Vitamin D Supplements

So you're finally considering adding a daily vitamin D supplement to your routine. Boosting your intake of the all-important sunshine vitamin has well-documented perks. But any time you adjust your supplement routine, it's important to understand potential effects - and how to avoid overdoing it.

When taken regularly, a vitamin D supplement can help ensure you're getting enough of the key vitamin so your body can function at its best.*

Plus, you may even notice a few positive effects of vitamin D that'll make you extra happy you decided to commit to striving for optimal levels.

Here's a breakdown of what to know about vitamin D supplements, the effects of vitamin D in the body, and how to make sure your routine is working for you. 

Newsflash: Most of us don't get enough vitamin D—like, not even close to enough.* (Research1 shows that roughly 1 billion people world wide are flat-out deficient by clinical standards, and that statistic considers all inputs like the diet, sun, etc.)

And while you can certainly try to add more fatty fish to your diet (which provides some vitamin D) and spend more uninterrupted time in the sun, taking a vitamin D supplement is almost always necessary to get optimal amounts D (i.e., achieve vitamin D sufficiency and stay there).*

In fact, according to Sina Gallo, Ph.D., RDN, a nutritional sciences professor at the University of Georgia, the reality is that it's actually quite difficult to get all of the vitamin D you need just from diet and sun alone.*

When your body produces vitamin D in response to sun exposure, it basically naturally shuts down production (and increases its metabolism) after getting its fill, according to Gallo. That's why lifeguards, for example, don't experience vitamin D toxicity, she says.

However, this isn't how it works when you get your vitamin D from food or supplements—in which case, it is technically possible (albeit much more challenging than you might think) to get too much, she says.

Typically, the first sign that you're in vitamin D overdrive is hypercalciuria, or too much calcium in your urine. This is usually accompanied by hypercalcemia, or too much calcium in your blood, Gallo explains. Over time, this can contribute to kidney and blood vessel issues.

But unless you're taking mega (like mega) amounts of the vitamin, vitamin D toxicity isn't really a concern, and the totality of science to back this fact2 is compelling.

Case in point: One study in Canadians3 found that while taking 20,000 IU of vitamin D3 daily (more than 100 times4 the amount most people consume daily) did successfully increase whole-body vitamin D levels, participants didn't even come close to levels associated with toxicity.

As mbg's vice president of scientific affairs, Ashley Jordan Ferira, Ph.D., RDN, explains further, "Just because vitamin D is fat-soluble by design doesn't mean it's toxic at clinically useful doses, like 5,000 IU. That's a complete misnomer. In reality, true reports of vitamin D toxicity with clinical evidence2 have occurred at 200,000 to 300,000 IU per day—yes, you read that correctly—in vulnerable populations like infants of folks with medical issues." So, rest assured.

Adding a vitamin D supplement to your routine can help you support healthy vitamin D levels, which promotes bone, teeth, muscle, immune, and whole-body health.* Here are just a few of the positive side effects you may experience as you strive for optimal vitamin D intake:*

Because vitamin D facilitates (actually, it's critical for) the body's absorption and balance of calcium and phosphorus, supplementing your vitamin D intake can support these essential minerals in the various roles they play in the body, including bone health (which includes your teeth, too!), according to Gallo.*

Since calcium also plays a role in muscle function, checking that vitamin D box helps there, too. In fact, a comprehensive review of clinical trials5 revealed a link between supplementing with vitamin D3, specifically, and muscle strength.* Good news for anyone looking to support their movement routine!

An exciting area of research, clinical trial research clearly demonstrates that vitamin D sufficiency and supplementation (to achieve sufficiency) have a positive impact on long-term glycemic control6, insulin sensitivity7, and even one's metabolic health trajectory8.*

Science has established a pretty strong connection between vitamin D and mental well-being.* In fact, according to a 2020 review9, multiple clinical studies have identified the link, even highlighting that those with mood health needs have been seen to have lower vitamin D levels. Other evidence suggests that vitamin D supplementation may help reduce negative emotions10.*

Though too much vitamin D is far from a concern for the average person (but of course, partner with your health care provider to be sure), your tipoff that you might be too high in the D department, according to Gallo, is hypercalcemia (remember, that's too much calcium in your blood, determined by a blood test at the doctor's office).

According to the National Institutes of Health11, some of the first signs of hypercalcemia include:

If you experience any of these, check in with your health care provider, stat.

Because so many people don't come close to getting enough vitamin D through food and sunshine alone, a high-quality supplement can be incredibly helpful (if not essential) in achieving healthy vitamin D levels and the corresponding immune, bone, muscle, and whole-body benefits.*