The Benefits vs. Side Effects of Vitamin D

Vitamin D, also known as calciferol, is a fat-soluble vitamin essential for physical and mental health. The two primary forms of vitamin D are vitamin D2 (ergocalciferol), found in plants, and vitamin D3 (cholecalciferol), found in animal tissues.

Vitamin D is essential for immune system function and bone health. It may also influence mood regulation and reduce the risk of several chronic health conditions.

This article looks at vitamin D's benefits and side effects, deficiency symptoms, and how much you should consume each day.

Woman cooking salmon with spinach and mushrooms

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Effect of Vitamin D on the Body

Vitamin D helps the body retain and absorb calcium and phosphorus, which are important for building and maintaining healthy bones and teeth. Your nerves need vitamin D to carry messages between your brain and body, your immune system needs it to fight off bacteria and viruses, and your muscles need it to move.

Studies have shown that vitamin D may affect our mental health by reducing negative emotions. Researchers noted that individuals with major depressive disorder and vitamin D deficiency are most likely to benefit from supplementation.

Vitamin D deficiency can lead to decreased bone density, which can eventually cause osteoporosis and broken bones. In adults, a severe deficiency can also result in osteomalacia, which causes muscle and bone pain and weakness.

While more research is needed, several studies link vitamin D deficiency to several health conditions, including:

Vitamin D and Children

Vitamin D is important for children because it helps build strong bones and protects against rickets. This rare condition affects bone development, primarily in the first two years of life. The vitamin also protects against broken bones in children and teens.

Different Ways to Get Vitamin D

Your body makes vitamin D when it’s exposed directly to sunlight. However, prolonged sun exposure is advised against because it can increase your risk of other ailments, such as premature aging and skin cancer. Additionally, most people get less vitamin D during the winter months because of insufficient exposure to sunlight.

This makes it necessary to get vitamin D from other sources. Because vitamin D is not naturally present in many foods, fortified foods provide most of the vitamin D in the American diet.

Dietary sources of vitamin D include:

  • Fatty fish, such as tuna, salmon, and mackerel
  • Mushrooms
  • Egg yolks
  • Beef liver
  • Cheese
  • Fortified dairy products
  • Fortified breakfast cereals and orange juice

What Are Signs You Need Vitamin D?

Vitamin D deficiencies are relatively common throughout the United States. Many people with vitamin D deficiency have no symptoms. However, a deficiency may cause the following symptoms:

Risk Factors

You may have a greater risk of developing vitamin D deficiency if you take medications that interfere with vitamin D metabolism or if you have the following conditions:

  • A history of gastric bypass surgery (a type of weight-loss surgery)
  • Celiac disease (immune reaction to the protein gluten found in wheat, barley, and rye)
  • Osteoporosis (reduced bone mineral density causing weak and brittle bones)
  • Chronic kidney disease or liver disease
  • Crohn's disease (an inflammatory bowel disease causing chronic inflammation of the digestive tract)
  • Sarcoidosis (autoimmune disease causing collections of inflammatory tissue in parts of your body)
  • Histoplasmosis (infection caused by breathing in fungal spores)
  • Tuberculosis (infectious lung disease mainly caused by a bacterium)
  • Hyperparathyroidism (parathyroid glands release too much hormone, raising calcium levels)

Your healthcare provider can order a blood test to measure the level of vitamin D in your blood. If your levels are low, your provider will likely recommend taking a vitamin D supplement to correct the deficiency.

Side Effects of High Vitamin D Levels

Vitamin D toxicity is unlikely to occur from diet or excess sun exposure since your body can control the amount of vitamin D it makes from the sun. In most cases, toxicity occurs due to the overuse of vitamin D supplements.

The main side effect of vitamin D toxicity is a condition called hypercalcemia, in which too much calcium builds up in the blood, causing symptoms like:

  • Nausea, vomiting
  • Confusion
  • Muscle weakness
  • Decreased appetite
  • Generalized pain
  • Excessive thirst and urination
  • Dehydration
  • Kidney stones

Extremely high vitamin D levels can cause more serious side effects, including irregular heartbeat, kidney failure, and death.

Dosing Vitamin D

Vitamin D intake is measured in international units (IU) and micrograms (mcg). The amount of vitamin D you need daily depends on your age and other health factors.

The daily vitamin D requirements are:

Life Stage Daily Recommended Amount
Birth to 12 months 400 IU (10 mcg)
Children 1–18 years old 600 IU (15 mcg)
Adults age 19–70 600 IU (15 mcg)
Adults over age 70 800 IU (20 mcg)
Pregnant and breastfeeding people 600 IU (15 mcg)

When to Take Vitamin D: Morning or Night?

Though some anecdotal reports claim that taking vitamin D before bed suppresses melatonin production and negatively impacts sleep quality, there is no solid evidence to support this theory. You can take vitamin D supplements any time of the day.

However, because vitamin D is a fat-soluble vitamin, it is best taken with meals or snacks containing fat, which helps your body better absorb the vitamin.


Vitamin D is involved in many bodily functions and plays a vital role in immune health and maintaining healthy bones and teeth. It may also help improve mood and protect against certain diseases. Vitamin D is found in some food products, such as fatty fish and fortified dairy foods.

The potential benefits of vitamin D supplementation are more significant in people with a confirmed vitamin D deficiency. Boost your vitamin D intake by making simple dietary changes, spending a safe amount of time in the sun, eating a balanced diet, and taking supplements.

Frequently Asked Questions

  • Does vitamin D give you energy?

    Vitamin D deficiency can cause fatigue. Studies have shown that vitamin D supplementation may improve fatigue in otherwise healthy individuals with vitamin D deficiency.

  • When does vitamin D start working?

    It usually takes a few months to raise vitamin D levels with consistent supplementation.

  • What do low vitamin D levels feel like?

    Symptoms of low vitamin D levels can include fatigue, muscle pain or weakness, bone pain, depression, and cognitive impairment.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. National Institutes of Health. Vitamin D : Consumer fact sheet.

  3. Cheng Y, Huang Y, Huang W. The effect of vitamin D supplement on negative emotions: A systematic review and meta‐analysisDepress Anxiety. 2020;37(6):549-564. doi:10.1002/da.23025

  4. MedlinePlus. Vitamin D deficiency.

  5. American Academy of Pediatrics. Vitamin D for babies, children & adolescents.

  6. National Institutes of Health. Vitamin D: Health professional.

  7. Nowak A, Boesch L, Andres E, et al. Effect of vitamin D3 on self-perceived fatigue: A double-blind randomized placebo-controlled trialMedicine. 2016;95(52):e5353. doi:10.1097/MD.0000000000005353

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By Lindsey DeSoto, RD, LD
Lindsey Desoto is a registered dietitian with experience working with clients to improve their diet for health-related reasons. She enjoys staying up to date on the latest research and translating nutrition science into practical eating advice to help others live healthier lives.