Do You Need a Vitamin D Supplement?
Diet & NutritionNutrients & Supplements

Do You Need a Vitamin D Supplement? Everything to Know

Do You Need a Vitamin D Supplement? Everything to Know
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Updated on October 21, 2025
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Note: The U.S. Food and Drug Administration (FDA) does not approve supplements for safety or effectiveness. Talk to a healthcare professional about whether a supplement is the right fit for your individual health, and about any potential drug interactions or safety concerns.

Vitamin D is known as the sunshine vitamin because it’s produced inside the body when rays of sun hit the skin. But sunlight isn’t the only way to get vitamin D. It’s found in a limited number of foods, but it’s not easy to consume enough of it through diet alone.

 This is one reason why many people take vitamin D supplements.
People who have suboptimal levels of this vitamin — roughly three-quarters of people globally — may also have underlying health conditions, such as kidney dysfunction, poor absorption in the digestive tract, milk allergy, or lactose intolerance. It can also happen when you follow an ovo-vegetarian or vegan diet. People in colder, northern regions have higher deficiency rates, and women are more likely to be deficient.

Inadequate or deficient levels of vitamin D can be an issue for your health, since vitamin D helps the gut absorb calcium, which is necessary for strong and healthy bones.

Potential Health Benefits of Vitamin D

Vitamin D is also helpful in reducing inflammation and boosting immune function and cell growth.

 Since vitamin D plays a key role in many bodily functions, research has connected it to a variety of potential wellness perks.

1. May Lower Risk of Multiple Sclerosis

Research shows that people with vitamin D deficiency have a 54 percent higher risk of multiple sclerosis (MS), a neurological disorder, than those with sufficient levels, and the risk may be much lower when people take vitamin D supplements.

The benefits may not translate into treating the disease. Research shows that vitamin D may help prevent MS, but it doesn’t appear to improve disability or reduce relapses in MS patients. In fact, too much vitamin D can lead to symptoms like fatigue, bladder problems, and muscle weakness, which may mimic MS symptoms.

Be sure to speak to your doctor if you have MS or a vitamin D deficiency to determine the right approach for your health concerns.

2. May Protect Mental Health

Vitamin D is an antioxidant that has activity in brain tissue — and studies show low vitamin D levels are associated with increased symptoms of depression and anxiety. Researchers recommend that doctors check vitamin D levels as part of preventing and planning treatment around these mood disorders.

“Mental health and nutrition are closely connected,” says Maxine Yeung, RD, the owner of The Wellness Whisk in the San Francisco Bay Area. “A link between vitamin D deficiency and increased symptoms of depression and anxiety highlights the importance of meeting nutrient needs to help support one’s emotional well-being.”

One review of 18 clinical trials found that vitamin D supplements helped lower depression symptoms slightly, but only in people who already have adequate vitamin D levels. That means if you’re deficient, your levels may need to be corrected before you see the added benefit of vitamin D supplementation. More research is needed to determine effective dosing.

3. May Help Cancer and Chronic Disease Outcomes

Vitamin D could be one pathway to reducing the impact of cancer, although current research is mixed.

One review found that vitamin D intake may help prevent breast, colorectal, and lung cancer, and may even reduce colon cancer mortality. That said, results for other cancers are inconsistent or unavailable.

In another randomized controlled trial of more than 25,000 participants, those who took 2,000 IU of vitamin D did not have a lower rate of cancer or cardiovascular events than the placebo group. But those who developed cancer had a 25 percent lower death rate when they were taking vitamin D.

“Understanding the role of vitamin D in preventing chronic diseases is important when determining the appropriate recommendation for supplementation,” says Yeung. “This study shows that in generally healthy adults, regular vitamin D supplements may not help reduce the risk of cancer, however, there may be benefits for those with cancer.”

The findings also included a possible reduction in cancer risk for African Americans, which researchers say warrants further study.

Weight Loss Effect of Vitamin D

Low vitamin D levels are linked to obesity, but research doesn’t show that vitamin D supplementation may help with weight loss. The two have a complex and not yet fully understood relationship.

“There are so many factors, from genetics to environment to lifestyle, that influence weight, so it’s unrealistic to expect a single nutrient to lead to weight loss,” says Yeung. “However, supplementing with vitamin D may indirectly support weight loss by improving mood and energy levels in those with depression, potentially making it easier to maintain healthier lifestyle habits.”

Potential Risks and Side Effects of Vitamin D

If you take too much supplemental vitamin D, it can lead to toxicity as well as other possible problems.

 You can’t get too much vitamin D from the sun, since your skin limits the amount of vitamin D it produces.

 (You should always take precautions with sun exposure.)

Risks

Since vitamin D is fat soluble, it’s stored inside the body — rather than being eliminated through urine — and can become harmful if there’s too much of it. If your doctor recommends it because your vitamin D levels are low, a daily dose of 2,000 to 4,000 IU per day is generally considered safe.

“Higher doses of 10,000 IU per day have been linked to decreased bone mineral density, increased risk of falls, and elevated calcium levels in blood and urine,” says Jessica Tosto, RDN, a clinical associate professor and department chair of nutrition and dietetics at Pace University in Pleasantville, New York.

Vitamin D can also interact with medicines such as the weight loss drug orlistat (Xenical and Alli), cholesterol-lowering statins, steroids like prednisone, and thiazide diuretics (like Hygroton, Lozol, and Microzide). Always tell your doctor which prescriptions and over-the-counter supplements you’re taking.

“Those who have had or are at risk for kidney stones should be cautious with very high-dose vitamin D supplements,” adds Tosto. Vitamin D may potentially increase the risk of kidney stones by influencing how calcium is processed by your body.

Side Effects

If you take too much vitamin D, you may experience symptoms such as:

Food Sources of Vitamin D

There aren’t many dietary sources of vitamin D, but there are foods and drinks that are fortified with it. Common options that contain this vitamin include:

  • Fish, such as freshwater trout, salmon, canned light tuna, and sardines
  • Dairy products, such as milk, yogurt, kefir, and cheese
  • Plant-based milks, such as almond, rice, or soy beverages
  • Vegetables and fruit products, such as mushrooms and fortified orange juice
But those relying on sourcing vitamin D through diet alone typically won’t meet their daily requirements. Even drinking an 8-ounce glass of milk will get you only 120 IU — 15 percent of the amount that many adults need daily.

How to Select Vitamin D

If you choose to go the supplement route, Kerry Hackworth, RDN, who helps clients with dietary needs in Chicago, recommends taking around 400 to 800 IU of vitamin D3 (cholecalciferol) per day. “Vitamin D3 is the form that is already stored in the body, so some studies have found it to be more effective,” says Hackworth. “Also, take vitamin D with a healthy fat, such as sliced avocado, because it is a fat-soluble vitamin that requires fat to be absorbed.”

The potency of supplements varies greatly among brands. One older study found that supplements had between 9 and 146 percent of the expected dose. The researchers found supplements from a USP-verified bottle were the most accurate and least variable.

 Before buying a supplement, check the label for approval from USP, NSF, or ConsumerLabs. This means the product has undergone third-party testing for quality and purity.
Since D3 sometimes comes from animal sources, vegans should opt for vitamin D2 or a D3 supplement marked as vegan.

Dosage of Vitamin D

Adults need 600 international units (IU) of vitamin D each day (800 IU if you’re over age 70), which can be sourced through sunlight, diet, or supplements.

“It’s a good idea to get your baseline vitamin D level tested before considering high-dose vitamin D supplementation,” says Tosto. “For those who do not have vitamin D deficiency, a standard dose of 400–600 IU per day is sufficient.”

Vitamin D is crucial for bone health, immune support, and overall well-being. Discover our recommendations for the best vitamin D supplement that may ensure you’re getting the optimal benefits for your health.

The Takeaway

  • Vitamin D, a nutrient that helps build bones, supports immunity, and keeps brain cells healthy, comes from sunlight, a limited number of foods, and supplements. Most people worldwide are deficient.
  • Supplements might help you meet your daily needs, which may have benefits in lowering the risk of certain health conditions, including multiple sclerosis, depression and anxiety, and potentially cancer mortality.
  • Excessive vitamin D can cause toxicity, high calcium levels, kidney stone risk, and side effects like nausea or confusion. Talk to your healthcare provider about the right dose for you.

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Sylvia Klinger, DBA, MS, RD, CPT, is an internationally recognized nutrition expert who is relentlessly passionate about helping people fall in love with creating and enjoying delicious, safe, and nutritious foods.

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