Vitamin D: what is it, proper levels, benefits, side effects

last updated: Oct 27, 2021

5 min read

Back in the ‘90s, every time you turned on the TV or opened a magazine, there was a good chance you’d come across some popular celebrity with a milk mustache. The “Got milk?” ad campaign, designed to encourage people to drink more milk to boost their vitamin D and calcium, was quite successful—at least for milk distributors. But many people still don’t get the vitamin D they need.  

If you can’t stomach large amounts of milk to get more vitamin D, you’re not alone. Fortunately, there are other ways to get your levels in a healthy range. Find out why this vitamin is essential for your health and the steps you can take to ensure you’re getting the amount you need.

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What is vitamin D?

Vitamin D is a nutrient your body needs to grow and stay healthy. It is essential for maintaining healthy bones and muscles, as well as many other functions in the body. 

People get vitamin D through sun exposure, foods, and supplements (NIH, 2021): 

  • Sun exposure: Your skin produces vitamin D when exposed to UVB (ultraviolet B) rays from the sun. But older age, darker skin, and the use of sunscreen can all limit vitamin D production. While the sun can be a significant source of vitamin D, limiting your exposure is important to reduce your risk of skin cancer, so this isn’t necessarily the best source of vitamin D for most people. 

  • Food sources: Only a few foods naturally contain vitamin D. These include fatty fish like trout, salmon, tuna, mackerel, and sardines, cod liver oil, egg yolks, and mushrooms. Most people get the bulk of their dietary vitamin D from fortified foods (food with vitamin D added), such as milk (both dairy and plant-based), cereal, orange juice, and certain yogurts. 

  • Supplements: Despite the availability of fortified foods, most Americans don’t get the recommended amount of vitamin D. Vitamin D supplements, including multivitamins that contain vitamin D, can help you meet your nutritional goals. 

Health benefits of vitamin D

Vitamin D receptors are present in most cell types in your body (Lordan, 2021). While scientists are still discovering all the effects of vitamin D, here’s what we know so far:

Bone health

Vitamin D is essential for maintaining strong bones by helping your body absorb calcium—a major component of bones. Long-term calcium and vitamin D deficiency can increase your risk of developing osteoporosis, especially as you age. Osteoporosis makes your bones weak, brittle, and more prone to breaking (NIH, 2021) 

Children who don’t receive enough vitamin D may develop rickets—a condition that softens bones and can cause bone pain, bone deformities, and problems with development. A similar condition called osteomalacia can occur in adults with chronic low levels of vitamin D (NIH, 2021). 

Other conditions

The role of vitamin D has been investigated for many other medical conditions, but our understanding is still somewhat limited. Studies have shown conflicting results associating vitamin D levels with the development of cancer, high blood pressure, and high cholesterol. Some studies showed an increased risk of developing multiple sclerosis (MS) or depression with low vitamin D levels, but giving vitamin D didn’t seem to help with treatment. Research has consistently shown that vitamin D does not help prevent or treat diabetes, nor does it help with weight loss (NIH, 2021). 

Vitamin D levels

If you’re concerned about your vitamin D intake, your healthcare provider can measure your levels with a blood test. The test measures levels of 25-hydroxyvitamin D—the main form of vitamin D found in your blood (NIH, 2021). 

  • Levels of at least 50 nmol/L (20 ng/mL) are considered adequate for bone and overall health in most adults. 

  • Levels below 30 nmol/L (12 ng/mL) in an adult are associated with vitamin D deficiency and can weaken your bones and affect your health. 

  • Levels above 125 nmol/L (50 ng/mL) in adults are too high and may cause health problems. 

So how much vitamin D do you need? 

The National Academy of Medicine (NAM; previously the Institute of Medicine) has developed recommendations for the amount of vitamin D healthy people should consume. These values are called Recommended Dietary Allowances, or RDAs. 

For people 1–70 years old, the RDA for vitamin D is 600 IU (15 mcg). Individuals over 70 should aim for 800 IU (20 mcg) per day. While we don’t have enough evidence to develop an RDA for infants under one, the NAM recommends babies receive 400 IU (10 mcg) daily. These recommendations assume that all vitamin D comes from dietary sources, and sun exposure was not considered (Ramasamy, 2020). 

Your healthcare provider may recommend a different amount of vitamin D depending on your medical conditions and risk factors. 

Vitamin D deficiency

Some people are at an increased risk of developing vitamin D deficiency. Your healthcare provider may monitor your vitamin D levels and recommend taking a supplement to meet your needs. Groups at increased risk include (NIH, 2021; Ramasamy, 2020):

  • Breastfed infants, as vitamin D does not travel into breastmilk well 

  • People who have obesity or have undergone gastric bypass surgery 

  • Older adults 

  • People who use certain seizure medications, including phenobarbital, carbamazepine, phenytoin, and valproate 

  • People with chronic kidney disease 

  • People with conditions that affect fat absorption, such as cystic fibrosis, celiac disease, Crohn’s disease, ulcerative colitis, and certain forms of liver disease 

  • People with limited sun exposure, such as those in nursing facilities or who are homebound 

Vitamin D supplements

Vitamin D supplements come in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). While most experts agree that vitamin D3 raises levels better and for longer, both are effective options (NIH, 2021). 

Vitamin D is found in stand-alone products, as well as other supplements, including fish oil, cod liver oil, and multivitamins. Always read the label of all the products you take to ensure you are not consuming too much vitamin D. 

Side effects

Side effects from vitamin D are uncommon, but too much vitamin D can cause problems. Vitamin D toxicity can cause your calcium levels to become too high (hypercalcemia) and lead to nausea, vomiting, muscle weakness, pain, loss of appetite, dehydration, and kidney stones (NIH, 2021). Follow your healthcare provider's instructions and pay close attention to whether your vitamin D dose is weekly or daily. Also, be sure to let your healthcare provider know about all the supplements you take so they can ensure your vitamin D dose is appropriate. 


Doses of vitamin D for most people looking to maintain healthy levels typically range from 600–1000 IU (15-25 mcg) per day. 

If you have vitamin D deficiency, you’ll likely need higher dosing to raise your levels. Your healthcare provider may recommend a regimen that starts with weekly vitamin D doses as high as 50,000 IU for 6–12 weeks, followed by daily doses of 800–2000 IU (Ramasamy, 2020). 

Maintaining your vitamin D levels in a healthy range keeps your bones strong and is important for overall health. Your nutritional status affects every part of your body, so eating a well-balanced diet, and supplementing when needed, is essential. Talk with your healthcare provider if you have any concerns about your vitamin D status. A simple blood test can let you know where you stand and if your intake needs to be adjusted. 


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

October 27, 2021

Written by

Christina Varvatsis, PharmD

Fact checked by

Steve Silvestro, MD

About the medical reviewer

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.