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Vitamin D: Benefits, Deficiency, Sources, Dosage, and Safety

Written by Lauren Panoff, MPH, RD

Reviewed by Anthony Dugarte, MD 

Last Updated on May 26, 2021

Understanding what vitamin D does in your body, how much is recommended, and the best places to get it can help you make sure you’re getting enough.

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Vitamin D: Benefits, Deficiency, Sources, Dosage, and Safety

Vitamin D has long been known as “the sunshine vitamin.” Our understanding of this important vitamin has grown significantly, particularly during the COVID-19 pandemic, as an important nutrient for immune health.

What Is Vitamin D?

Vitamin D is different from other vitamins. It is often called an immunomodulatory hormone as it acts more similarly to hormones.

Some of its main roles include maintaining skeletal strength, supporting gut integrity, optimizing immunity, and helping to regulate calcium metabolism in your bones.

Vitamin D comes in two main forms: vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol.

The biggest difference between the two is that ergocalciferol is made by plants, and cholecalciferol is produced by animals.

Furthermore, cholecalciferol tends to be better utilized by the body.

Therefore, this form is more commonly prescribed for increasing blood levels of vitamin D, particularly for the purpose of treating a deficiency.

Alongside vitamins A, E, and K, vitamin D rounds out the fat-soluble vitamin category.

While the water-soluble B and C vitamins dissolve in water and are excreted in excess by your body, the fat-soluble vitamins act more like oil. They are more likely to accumulate in your adipose tissues and liver.

Additionally, the fat-soluble vitamins are best absorbed and utilized by your body when you eat them with dietary sources of fat.

Six Health Benefits of Vitamin D

Because vitamin D is deeply involved in so many everyday processes within your body, it’s no surprise that getting enough of it is imperative to experience the most health benefit.

According to research, some of the main benefits of vitamin D include the following:

1. May Support Healthy Weight Maintenance

According to a 2017 review, lower vitamin D status is frequently found among obese individuals regardless of geographic location, ethnicity, and age, although it doesn’t always indicate a clinical problem.

And a 2021 review notes that data consistently support an inverse association between serum vitamin D levels and body weight but that more research is needed to determine whether supplementation may aid in healthy weight loss.

However, in a 2009 randomized controlled trial among 63 overweight or obese women, researchers found that those who took daily calcium plus vitamin D supplement over 15 weeks lost more weight compared to those who were given a placebo.

This was attributed to the appetite-suppressing effects of the additional vitamin D and calcium in the participants’ diets.

2. May Support Heart Health

Vitamin D is involved in a number of processes that are related to heart health and function.

Some research has suggested that not having enough vitamin D may increase the risk for heart disease.

Low blood levels of vitamin D have been associated with inflammation, higher coronary artery calcium scores, impaired endothelial function, and arterial stiffness.

Some longitudinal studies have even found a higher incidence of cardiovascular mortality and morbidity in the presence of vitamin D deficiency.

While more research on the relationship is needed, some observational studies have found that vitamin D deficiency is often associated with higher blood pressure levels, a risk factor for heart disease when unmanaged.

3. Boosts Your Immune Defense

Research has demonstrated that vitamin D is likely involved in linking your innate and adaptive immunity, making sure that your immune system properly recognizes and responds to initial threats and remembers how to respond to them later.

What’s more, both of these processes appear to be hindered by vitamin D deficiency.

In a 2017 meta-analysis of 25 randomized controlled trials involving over 11,000 participants ages 0–100 years, researchers found that vitamin D supplementation was able to reduce the risk for acute respiratory infections among people with a higher susceptibility to them.

Supplementation was even more successful among people who had vitamin D deficiency at the beginning of the study.

A 2020 review in the journal Nutrients found that vitamin D deficiency appears to increase your risk for immune-related disorders, such as sepsis, respiratory infections, psoriasis, type 1 diabetes, multiple sclerosis, rheumatoid arthritis, tuberculosis, and COVID-19.

Vitamin D supplementation may also help reduce your risk for more common illnesses as well, such as seasonal influenza A, as demonstrated by a 2010 study among children who received supplementation throughout the winter.

4. May Help Improve Mood and Cognitive Function

In a 2008 randomized controlled trial among 441 adults, researchers found that there appears to be a relationship between serum vitamin D status and reported symptoms of depression.

Both groups who were given either 20,000 or 40,000 IU of vitamin D per week for one year reported an improvement in depression symptoms compared to the control group, who was given a placebo supplement.

In another 2007 study, researchers found that vitamin D deficiency was more common among people who were experiencing anxiety and depression.

And in a 2013 review of 13 studies, the authors concluded that low blood levels of vitamin D are often associated with an increased risk for depression.

Furthermore, vitamin D deficiency may increase susceptibility for neurodegenerative diseases like Alzheimer’s dementia, as well as poorer cognitive function in older people.

5. Promotes Strong Bones

Vitamin D has a strong role in regulating nutrients important for skeletal health.

Plus, vitamin D deficiency has been linked to an increased risk for osteomalacia and osteoporosis, two metabolic bone diseases.

In a 2016 meta-analysis of randomized controlled studies by the National Osteoporosis Foundation, researchers found that calcium plus vitamin D supplementation is warranted for the prevention of fractures among middle-aged to older adults.

A more recent 2019 review published in JAMA Network Open concluded that, after examining data from 11 observational studies and over 39,000 participants, the combination of calcium plus vitamin D supplementation was a promising strategy for reducing fracture risk.

6. Helps Manage Blood Sugar

Some research has suggested that deficiency of vitamin D increases diabetes risk.

This is because one of the roles of vitamin D is to maintain the normal release of insulin by pancreatic beta cells.

Additionally, vitamin D appears to help your body better absorb and utilize calcium, which in turn helps regulate insulin secretion.

While more research is needed, in a 2015 study, supplementation of vitamin D was found to be successful for improving blood sugar control and preventing common complications among people with type 2 diabetes.

How Much Vitamin D Do You Need?

For most healthy people, meeting vitamin D needs can be achieved through a combination of safe sun exposure, dietary sources, and appropriate supplementation where needed.

But how much should you be aiming to get daily?

The recommended dietary allowance (RDA) for vitamin D is as follows:

  • 0–12 months: 10 mcg (400 IU)
  • 1–18 years: 15 mcg (600 IU)
  • 19–70 years: 15 mcg (600 IU)
  • Over 70 years: 20 mcg (800 IU)

The most accurate way to tell whether you’re getting enough vitamin D is to have your blood levels checked at your next wellness visit.

Vitamin D levels can vary significantly between people, and there are a number of factors that influence how much you may absorb from sunlight.

Knowing your baseline blood levels can help make sure you’re supplementing appropriately if needed, including identifying whether a prescription dose of vitamin D is needed to correct a deficiency.

Still, deficiency is widespread all over the globe. If you’re unable to get your blood levels checked for a while, and you suspect you may need to increase your vitamin D intake, a moderate vitamin D supplement may be recommended.

According to a 2008 study, supplementing 1,000–1,500 IU of vitamin D per day can help most people maintain adequate serum levels.

It’s important not to go overboard with vitamin D supplementation, as more is not always better. Vitamin D is a fat-soluble vitamin and comes with a risk for toxicity.

The upper daily limit is 4,000 IU. If taken in such a high amount over an extended period, vitamin D can put you at risk for hypercalcemia, kidney damage, and dehydration.

A serum vitamin D level above 375 nmol/L (150 ng/mL) is considered toxic.

Vitamin D Deficiency

Data shows that nearly half of people worldwide are deficient in vitamin D.

As mentioned, the best way to determine whether you’re deficient is to have a simple blood test performed by your doctor.

Optimal vitamin D levels in your blood are generally at least 50 nmol/L, and a reading that falls below 30 nmol/L is generally considered a deficiency.

Untreated and prolonged vitamin D deficiency may raise your risk for heart disease, certain cancers, bone loss, depression, and increased susceptibility to illness and infection.

Best Sources of Vitamin D

A combination of moderate, safe sun exposure, fortified foods, and appropriate supplementation as needed is the best approach to meeting your vitamin D requirements for most healthy people.

Vitamin D from the Sun

Vitamin D is sometimes called “the sunshine vitamin” because some of it is produced by your skin when exposed to direct UVB sunlight.

UVB rays trigger your skin to convert a compound called 7-dehydrocholesterol into the active form of vitamin D3.

This process involves metabolizing vitamin D into 25-hydroxyvitamin D3 in the liver and ultimately into 1-alpha, 25-dihydroxyvitamin D3 in the kidneys.

At that point, vitamin D can then be utilized effectively in your body.

Still, even if you spend a lot of time outdoors, there are several factors that determine how much your skin can make.

Some of these include sex, age, geographic location, and skin pigmentation.

Vitamin D Foods

Unfortunately, most foods aren’t very good sources of vitamin D. As a result, most people are only getting 5–10% of their vitamin D requirements from their diet.

Some of the most widely consumed food sources of vitamin D are fortified foods, like dairy or plant-based milk products, and certain breakfast cereals.

The nutrition facts label on these foods will tell you whether and how much vitamin D has been added to them.

Other food sources of vitamin D include:

Egg Yolks
Egg yolks appear to be higher in vitamin D if they came from free-range chickens who spent more time in direct sunlight, compared to conventionally raised chickens. The amount may also depend on how much vitamin D was added to the chicken’s feed.

Fatty Fish
Fatty fish, such as mackerel, salmon, and herring. Canned fish, like sardines and tuna, contain small edible bones that naturally contain vitamin D.

UV-Treated Mushrooms
UV-treated mushrooms are grown in the presence of UV light, unlike most traditional mushrooms found in grocery stores.

Vitamin D Supplements

Unless you’re eating vitamin D-containing foods on a daily basis and getting adequate direct sunlight, the most consistent source of vitamin D for most people is in the form of a supplement.

The top three priorities when purchasing a vitamin D supplement include quality, dosage, and form.

Quality
It’s best to choose a dietary supplement that has been third-party tested by an unbiased outside body and bears a reliable seal indicating such.

Some examples include NSF International, ConsumerLab, USP, and Informed Choice.

Depending on the seal, this may indicate that the product has been verified to contain what it says in the amounts listed and was not found to contain potentially harmful contaminants, for example.

Dosage
More is not always better, especially when it comes to fat-soluble vitamins that come with a risk for overdose and toxicity.

Getting your baseline serum vitamin D levels through a blood test is the best way to help determine an appropriate dose.

For most people, a daily dose of between 1,000–1,500 IU per day can maintain serum levels, but higher doses may be indicated to correct a deficiency.

Form
Vitamin D3, or cholecalciferol, is more effective than ergocalciferol, or vitamin D2, for increasing blood levels of vitamin D.

Additionally, D2 tends to be more sensitive to environmental factors and may degrade more easily over time in storage.

Keep in mind that if you’re vegan, D2 is always derived from plants, whereas D3 is more commonly made from lanolin, the oil produced by sheep’s wool.

However, there are some lichen-derived vegan D3 supplements.

Vitamin D Safety Considerations

The main safety consideration when it comes to vitamin D is making sure that you’re not going overboard.

The fat-soluble nature of vitamin D makes it important to be aware of the risk for toxicity, particularly if you’re using a supplement.

High levels of vitamin D can increase the risk for high levels of calcium in the blood, GI upset, or kidney damage.

The best way to be sure you’re supplementing appropriately is to speak with your doctor and have your blood levels tested.

The Bottom Line

Vitamin D is an important nutrient for your health. Getting enough vitamin D can help lower your risk for a number of chronic diseases, keep your bones strong, and optimize your immune defense against illnesses and infections.

It’s a good idea to have your blood levels of vitamin D tested to get a baseline and identify whether an intervention is needed to correct a deficiency.

For most people, a combination of vitamin D-containing foods, safe exposure to direct sunlight, and a moderate vitamin D supplement will be adequate for meeting your vitamin D needs.

Speak to your doctor to make sure you’re getting enough vitamin D and address any deficiency concerns.

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