Sunshine in a Capsule: Vitamin D Supplements Explained and Who Should Take Them

Vitamin D has been linked to maintaining cardiovascular health, according to a systematic review and meta-analysis published in July 2024. Specifically, vitamin D offers “overall beneficial effects on blood pressure, blood lipid levels and glycemic parameters.” This was especially the case in non-Westerners, participants with lower vitamin D levels, those with a BMI under 30 and adults aged 50 and older. 

Vitamin D is a key nutrient that supports healthy immune function and bolsters our bones, brains and more. Keep reading to learn about the benefits, potential risks and who should take vitamin D supplements. Remember, before you start taking any supplement, it’s important to consult your doctor to make sure it suits your health needs. 

What is vitamin D? 

Your body needs vitamin D for several critical processes, from building healthy bones to regulating certain cellular functions. It also affects your brain, skin and muscle function. 

As far as bone health goes, vitamin D plays an important role because it maintains calcium and phosphorus balance by promoting absorption. Vitamin D is usually added to milk to increase calcium absorption, which occurs in the small intestine. 

Vitamin D comes in two primary forms: D2 (ergocalciferol) and D3 (cholecalciferol). They function fairly similarly in your body, although D3 is more bioavailable and, therefore, more effective in raising and maintaining adequate vitamin D levels in the bloodstream. 

Good news: Your body actually has the ability to make vitamin D on its own when a chemical in your skin gets direct sunlight. Bad news: Most people can’t make as much vitamin D as their bodies need. This becomes particularly true with limited sun exposure during the winter months when the days shorten and you spend less time outdoors. Others at higher risk for developing vitamin D deficiency include those who have dark skin, fat malabsorption disorders, inflammatory bowel disease or are older adults. 

Without enough of this vitamin, you’re more prone to stress fractures. Some people also experience fatigue, aches and pains due to vitamin D deficiency. 

If you think you might have this deficiency, ask your doctor to order a blood test. They can help you determine if you’re low on this vitamin and, if so, the best way to increase your levels. Some people benefit from adding more vitamin D-rich foods and drinks to their diet, while others need vitamin D supplements. 

Foods with vitamin D 

If you want a safe, risk-free way to get more of this nutrient into your body, stock up on foods with vitamin D. Some naturally occurring sources include:

• Tuna
• Trout
• Salmon
• Sardines
• Herring
• Mackerel
• Egg yolk
• Mushrooms
• Shrimp
• Cheese
• Beef liver

You can also find foods and drinks fortified with vitamin D. Remember, your body needs vitamin D to adequately absorb calcium. As a result, you’ll often find it in milk and yogurt. Check the packaging. It should specifically say something like “fortified with vitamin D.” 

You might also find vitamin D-fortified cereals, oatmeal and orange juice. In other words, food manufacturers have seemingly decided that a healthy dose of vitamin D is a great way to start the day. Also, these foods are fortified because they are affordable and accessible to most people.

If you got a blood test and found that you’re low in this vitamin, you can try moving to a D-rich diet. If another test reveals that you’re still low, it’s likely time to start exploring vitamin D supplement benefits. 

Vitamin D benefits

Whether you combine food and sunlight or add vitamin D supplements to your diet, getting enough of this nutrient makes a big difference for your body. Specifically, sufficient vitamin D can deliver:

Stronger bones

Studies show that vitamin D plays a critical role in your body’s calcium absorption. And as you probably already know, calcium means strong, healthy bones. That’s why doctors often prescribe vitamin D supplements for kids with rickets and people with inherited bone disorders. 

Since everyone has bones, it’s worth double-checking that you’re getting enough vitamin D. Sufficient vitamin D can help prevent and manage osteoporosis.

Reduced risk of heart disease and diabetes

Across the country, heart disease is the leading cause of death. While many factors come into play here, studies have linked low levels of vitamin D and:

• Heart disease
• Stroke
• Hypertension
• Type 2 diabetes

If you’re looking for a way to defend yourself against some of the most common health conditions in the country, it might be time to consider these vitamin D supplement benefits. 

A stronger immune system

While low vitamin D levels can make you more likely to get sick, the opposite can also be true. This vitamin works to activate your T cells, which help your body fight infection. That means vitamin D supplement benefits can include a reduced likelihood of getting sick, along with the potential to shrink your risk for deregulated immune system conditions like rheumatoid arthritis, asthma and diabetes. However, more research is needed to fully understand the extent of vitamin D’s impact on these conditions. 

A more balanced mood

Studies link insufficient vitamin D and depression. What’s more, even if you’re not living with major depressive disorder, low levels of vitamin D can contribute to depressive symptoms like low mood and apathy. 

Reduced cognitive decline

Speaking of your brain, vitamin D might help it. Studies seem to demonstrate a correlation between vitamin D insufficiency and decreased cognitive function. Beyond that, early research suggests that low vitamin D levels can contribute to cognitive decline as we age. 

In short, those vitamin D supplements may help you stay sharp now and through the years. 

Drawbacks to vitamin D supplements 

All of this said, you can certainly have too much of a good thing regarding vitamin D supplements. 

While experts recommend around 600 international units (IU) of vitamin D a day for most adults, taking 4,000 IU a day or more is considered unsafe, particularly for those supplementing without a known vitamin D deficiency. These high doses, especially over a longer period of time, are linked to:

Hypercalcemia

Taking too much vitamin D can lead to hypercalcemia, which means you have too much calcium in your blood. This can cause kidney stones and contribute to hardening in your blood vessels, lungs and heart. 

Nausea and vomiting

Excess vitamin D supplements can upset your stomach, leading to nausea and vomiting. In fact, if you recently started taking these supplements and have been feeling queasy, it could be a sign that you’re overdoing it. 

Dehydration

Taking extremely high levels of vitamin D can cause toxicity. One of the primary symptoms of vitamin D toxicity is intense dehydration. 

Confusion

While some of the biggest vitamin D supplement benefits center around your brain, too much can cause the opposite effect. People taking an excess amount often report disorientation and confusion. 

Should you take vitamin D supplements?

Screening for Vitamin D is actually not currently recommended as evidence is “insufficient to assess the balance of benefits and harms of screening for vitamin D deficiency in asymptomatic adults,” per the US Preventive Services Task Force. Instead, doctors test more for diagnostic purposes — for instance, if someone has a suspicious symptom. If you have concerns, consult your doctor. 

If you are vitamin D-deficient, adjusting your diet may be enough to tip the scales. If you’re still low in this key nutrient after eating more D-rich foods or live in a climate where you’re not getting enough sunlight, supplements can help. Your body needs vitamin D to keep your bones strong, bolster your immune response and support your heart and brain health. Just make sure you keep an eye on your intake levels. Around 600 to 800 IU a day should be plenty, unless your doctor instructs you otherwise.

Can you take too much vitamin D?

According to the National Institutes of Health, too much vitamin D can be harmful. This is known as vitamin D toxicity or hypervitaminosis D. Over 375 nmol/L or 150 ng/mL of vitamin D in your blood are considered very high levels and can cause the following:

• Nausea
• Vomiting
• Muscle weakness
• Confusion
• Pain
• Loss of appetite
• Dehydration
• Excessive urination 
• Thirst
• Kidney stones

Extremely high levels of vitamin D can lead to irregular heartbeat, kidney failure and death. This is typically caused by taking too many vitamin D supplements. 

For adults aged 19 and up, for example, 100 mcg (4,000 IU) is the daily upper limit for vitamin D from all sources, including supplements, food and beverages. However, a doctor may recommend a different upper limit if you have a vitamin D deficiency.