Are There Side Effects of Vitamin D3?

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Has your doctor told you that you have low vitamin D levels? Have you considered taking vitamin D supplements? If so, you need to know what vitamin D is and how it affects your health. Vitamin D is a fat-soluble vitamin with several crucial functions in the body. So, your doctor may recommend taking vitamin D3 supplements to meet your daily requirements, help prevent certain conditions, or treat a condition you already have. However, it’s possible to take too much vitamin D, which can lead to detrimental side effects. Continue reading to learn more about the health benefits of vitamin D, where it comes from, and the side effects of vitamin D3.

What Is Vitamin D?

Vitamin D is a critical nutrient in many different processes in the body. One of the primary roles of vitamin D is promoting healthy, strong bones. It helps your body absorb and regulate calcium and phosphorus, two minerals essential for bone health. Without enough vitamin D, you have a higher risk of osteoporosis, a condition where your bones become fragile and more likely to break. Vitamin D is also needed to help your muscles, nerves, and immune system work properly.

Forms of Vitamin D

There are two forms of vitamin D found in foods and dietary supplements: vitamin D2 (“ergocalciferol”) and vitamin D3 (“cholecalciferol”). Both forms increase the amount of vitamin D in your blood. However, studies suggest that vitamin D3 is better at raising blood vitamin D levels than vitamin D2. Vitamin D3 is the form found in animal foods and is naturally produced by the body.

How Much Vitamin D Do You Need? 

Everyone needs vitamin D, but the requirements vary depending on age. The daily recommended intakes of vitamin D are:

  • Birth to one year old: 10 micrograms (mcg), or 400 international units (IU)
  • One to 70 years old: 15 mcg, or 600 IU
  • 71 years and older: 20 mcg, or 800 IU
  • Pregnancy and lactation: 15 mcg, or 600 IU

The Institute of Medicine established these numbers, but there is ongoing scientific debate about optimal vitamin D requirements to promote good health. 

Where Do You Get Vitamin D From? 

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Vitamin D is unique because the primary natural source is sun exposure. However, several factors affect how much vitamin D your body can produce from the sun, such as: 

Latitude and season

People living in northern climates cannot meet their vitamin D requirements through sun exposure in the fall and winter.

Skin pigmentation

People with darker skin are less efficient at producing vitamin D from the sun. 

Limited sun exposure or sunscreen use

Vitamin D synthesis through sun exposure requires spending time outside with your skin exposed without sunscreen. Please note that excessive sun exposure is not recommended due to its relationship to skin cancer. 


The skin’s ability to make vitamin D from the sun declines with age. 


You can also get vitamin D through your diet, but there are few natural food sources. The best food sources are oily fish, such as salmon, herring, and mackerel. Some other foods, such as red meat, beef liver, egg yolks, and mushrooms, also contain small amounts of vitamin D.

In the United States, many foods are fortified with vitamin D, including:

  • Milk
  • Breakfast cereals
  • Some brands of orange juice, yogurt, and margarine

Vitamin D supplements and multivitamins are other common sources of vitamin D.

These factors put many people at risk of having insufficient vitamin D. 

Who Should Take A Vitamin D Supplement? 

Anyone unable to meet their vitamin D requirements through sun exposure and their diet should take a vitamin D supplement. For some people, this may mean taking a supplement only in the fall and winter months.

Vitamin D supplements are also used to prevent or treat some conditions, including:

  • Osteoporosis: If you have osteoporosis, your bones lose density and mass, making you more likely to get bone fractures. Vitamin D supplements can both prevent and help manage osteoporosis.
  • Osteomalacia and rickets: If you have osteomalacia, your bones soften from a prolonged vitamin D deficiency. When present in children, this condition is called rickets. Vitamin D supplements are part of the treatment for osteomalacia and rickets to strengthen bones. Supplements also help to prevent these conditions. 
  • Inherited bone disorders: Disorders like familial hypophosphatemia prevent your body from absorbing or processing vitamin D.
  • Multiple sclerosis (MS): MS is a disorder where your immune system attacks your nerves. Taking vitamin D may decrease your likelihood of getting MS.
  • Psoriasis: Psoriasis is a skin disorder treated with multiple medications, including some that contain vitamin D.

How Much Is Too Much Vitamin D?

Having too much vitamin D can be toxic, so upper limits for daily intake have been set: 

  • Birth to six months old: 25 mcg, or 1000 IU
  • Seven to 12 months old: 38 mcg, or 1500 IU
  • 12 months to three years old: 63 mcg, or 2500 IU
  • Four to eight years old: 75 mcg, or 3000 IU
  • Nine years and older: 100 mcg, or 4000 IU
  • Pregnancy and lactation: 100 mcg, or 4000 IU

If you exceed these upper limits, you may have too much vitamin D in your blood. A vitamin D level of 125 nmol/L (50 ng/mL) or higher in your blood is too high. Remember that vitamin D toxicity can only occur from supplemental vitamin D intake. 

Side Effects of Excess Vitamin D

Vitamin D toxicity is rare and only occurs through excessive supplemental intake. The potentially dangerous side effects of toxicity are related to how vitamin D is involved in calcium regulation. Too much vitamin D can raise the amount of calcium in your blood (called hypercalcemia), causing the following side effects: 

  • Nausea and vomiting
  • Poor appetite and weight loss
  • Constipation
  • Weakness
  • Confusion
  • Abnormal heart rhythms
  • Kidney stones and kidney damage

What To Do If You Have Side Effects of Vitamin D3

If you suspect you have side effects from excessive vitamin D, stop taking your supplements, limit your calcium intake and visit your doctor. If your kidneys have been affected, you may be admitted to the hospital for intravenous fluids to improve your kidney function. Your doctor may also prescribe corticosteroids or bisphosphonates, which help reduce blood calcium levels.

What’s Next?

You can meet your vitamin D requirements through a combination of sun exposure, food intake (naturally occurring and fortified foods), and supplements. Your doctor may recommend taking vitamin D supplements if you have a condition that improves with supplementation, such as osteomalacia or osteoporosis. However, beware you may have side effects of vitamin D3 if you take too much.

Resource Links:

  1. “Familial Hypophosphatemia” via Rare Diseases
  2. “Osteomalacia” via MedlinePlus
  3. “Osteoporosis Overview” via NIH
  4. “Vitamin D” via Harvard School of Public Health
  5. “Vitamin D” via Mayo Clinic
  6. “Vitamin D” via NIH
  7. “Vitamin D Toxicity – A Clinical Perspective” via Frontiers in Endocrinology
  8. “What is vitamin D toxicity? Should I be worried about taking supplements?” via Mayo Clinic
  9. “Vitamin D and MS: Is there any connection?” via Mayo Clinic