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What is Vitamin D? Health Benefits & Dosage

Written by Ana Aleksic, MSc (Pharmacy) | Last updated:
Evguenia Alechine
Puya Yazdi
Medically reviewed by
Evguenia Alechine, PhD (Biochemistry), Puya Yazdi, MD | Written by Ana Aleksic, MSc (Pharmacy) | Last updated:

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Vitamin D is a fat-soluble vitamin that the skin makes upon exposure to direct sunlight. Read on to learn about the potential benefits of vitamin D supported by science and find out why maintaining normal blood levels is so important for good health.

What is Vitamin D?

Vitamin D is a fat-soluble vitamin the body needs to build and maintain strong bones. It helps absorb calcium in the gut, keeping calcium and phosphorus in balance to mineralize bones. Vitamin D also helps support immune balance [1].

Without enough vitamin D, bones can become thin, weak, brittle, or misshapen. Getting enough vitamin D prevents rickets in children and osteomalacia in adults. Along with calcium, vitamin D also helps protect older adults from osteoporosis [1].

Some scientists view vitamin D as a prohormone because it is involved in many metabolic processes in the body [2, 3].

The body naturally makes vitamin D when exposed to sunlight. Getting regular, moderate sun exposure is a safe way to maintain normal vitamin D levels during the summer months.

Vitamin D is also found in certain foods, such as fatty fish like salmon and sardines. Additionally, many vitamin D supplements are available on the market.

Many older adults don’t get enough vitamin D from sunlight. The elderly also tend to have poor vitamin D absorption and less elastic skin, which puts them at a higher risk of deficiency. Taking a supplement with vitamin D may be beneficial for bone health in such cases [1].

Taken at the recommended doses, vitamin D supplements are considered safe. However, taking too much can be harmful. Vitamin D supplements may also interact with prescription medications. Remember to talk to your doctor before supplementing!

Strong evidence points to the importance of vitamin D for maintaining strong bones. Supplementation may be beneficial in people who can’t get enough of this vitamin from sunlight and food.

Health Benefits of Vitamin D

It’s important to note that many of the studies regarding vitamin D are association studies, which means that deficiency is correlated with a certain issue but doesn’t necessarily cause that issue.

In many of these cases, the reason why people’s health is worse is because they aren’t getting enough sun, rather than being deficient in vitamin D. The sun has a lot of health benefits that are independent of vitamin D. Thus, low vitamin D is often more of a signal that someone isn’t getting enough sun, which is the real cause of the health problem.

1) Supports Bone Health & Helps Prevent Bone Disorders

Vitamin D maintains calcium and phosphorus balance in the body. Specifically, it promotes calcium and phosphorus absorption from the gut, calcium reabsorption in the kidney, and calcium mobilization in bone [4, 5, 6].

Vitamin D deficiency causes rickets in infants, young children, and adolescents and osteomalacia in adults [7, 3].

Osteomalacia and rickets attributable to vitamin deficiency are preventable with an adequate nutritional intake of this vitamin. Varying doses and treatment regimes have been described with the aim is to achieve a blood level between 20 and 50 ng/mL [8].

Additionall, low blood levels of vitamin D are associated with lower bone mineral density, mineralization defects, and an increased risk of bone loss or fracture in both men and women [9, 10, 11, 12].

Evidence supports the use of vitamin D and calcium supplements at the recommended doses for bone health in older people who are at risk of deficiency. Studies suggest this combination may reduce bone fractures [9, 10, 11, 12].

2) May Protect Against Cancer

Some studies found that sufficient vitamin D levels protect against some types of cancer and the risk of dying. Vitamin D may help prevent cancer by strengthening the immune response, but its cancer-preventive effects are still being researched. [13].

For example, some studies suggest that women who get more sun and eat foods high in vitamin D are less likely to get breast cancer, while other studies found no link. Large-scale studies should clarify these findings [14, 15, 16, 17, 18, 19, 20, 21, 22, 23].

According to limited research, maintaining higher vitamin D blood levels may also aid in colon cancer prevention. On the other hand, deficiency might increase prostate cancer risk. More research is needed before any conclusions can be drawn  [13, 24, 25, 26].

Studies about vitamin D and prostate and ovarian cancer have had mixed results. Therefore, It’s still uncertain whether vitamin D can help prevent pancreatic or ovarian cancer, though early studies hint at its potential [27, 28, 29, 30, 31, 32].

Normal vitamin D levels appear to be important for cancer prevention, but large-scale studies are needed to further explore this link.

3) Supports Sleep, Brain Health & Development

Normal vitamin D levels support emotional balance, cognitive function, and quality sleep [33, 34, 35, 36, 37, 38].

Additionally, vitamin D is important for brain developement, which is why pregnant women are advised to get at least 600 IU of vitamin D per day. Babies and children up to 12 months require 400 IU/day.

What’s more, vitamin D deficiency has been associated with a wide range of psychiatric and neurological diseases [39, 40, 41, 42].

According to some researchers, low levels of blood vitamin D are associated with low mood, memory problems, and dementia [35, 34, 43, 33].

Limited research suggests that normal vitamin D levels may be protective against Parkinson’s disease, though solid evidence is still lacking [44, 45, 46].

Though vitamin D seems to contribute to mental health and normal sleep patterns, more research is needed to determine the benefits of supplementation.

Vitamin D supports healthy brain development and cognition. Low levels have been linked with memory problems and low mood. The benefits of supplementation in these cases are still an active area of research.

4) Reduces Inflammation & Autoimmunity

Vitamin D helps reduce inflammation in the body. Studies have shown that it may act as an immune balancer. It has the potential to influence a wide range of immune problems, infectious and autoimmune diseases [47, 48].

So far, limited studies hint at the promising effects of vitamin D for the following inflammatory and/or autoimmune conditions:

  • Multiple sclerosis [49, 50, 51]
  • Psoriasis [52, 53]
  • Thyroid problems [54, 55]
  • Lupus [56, 57]
  • Rheumatoid arthritis [58]
  • IBD [59, 60]
  • Chronic obstructive pulmonary disease [61, 62]
  • Type 1 diabetes [63, 64, 65, 66]
  • Asthma [67, 68]

All in all, studies have confirmed that vitamin D deficiency is more common in people with these autoimmune, inflammatory, and allergic problems or tendencies. Nontheless, evidence is lacking to support vitamin D supplementation in the majority of the cases.

Vitamin D deficiency has been linked with autoimmune and inflammatory problems. The benefits of supplementing are still uncertain.

5) May Improve Fitness & Heart Health

Clinical evidence suggests that vitamin D plays a role in muscle metabolism and function [69].

Vitamin D may help strengthen muscles, improve fitness, and reduce the risk of falls in the elderly. Deficiency might make athletes more prone to injuries, according to some studies [70, 71, 72].

Additionally, vitamin D deficiency has been associated with increased risk of cardiovascular disease (including high blood pressure, heart attacks, peripheral arterial disease, and stroke) in several studies [73, 74, 75].

Though studies linked vitamin D deficiency with heart disease, supplementation might not have a protective effect. Additional studies are needed.

On the other hand, several studies have linked sun exposure, which increases vitamin D levels, to lower blood pressure. Limited evidence suggests that UVB therapy might also reduce blood pressure, though larger studies are needed [76, 77].

Vitamin D supports heart health and physical fitness. Sun exposure may help lower blood pressure, but vitamin D supplements probably don’t have a protective effect.

6) May Help Prevent Obesity & Metabolic Problems

Vitamin D helps the pancreas produce insulin, which controls sugar levels. Deficiency may impair this process and is common in people with type 2 diabetes [78, 79, 80, 64, 81, 82, 83].

Limited studies suggest vitamin D supplementation might lower the risk of type 2 diabetes, but the available evidence is sparse [63, 64, 65, 66].

Additionally, several studies found a link between low vitamin D levels and obesity. Higher blood levels might prevent people from obesity and metabolic syndrome, limited studies suggest [84, 85, 86, 87].

Vitamin D supports healthy insulin production and sugar control. Deficiency has been linked with type 2 diabetes and obesity, though more research is needed.

7) Helps Prevent Infections

Scientists discovered that people deficient in vitamin D are more likely to get tuberculosis. Limited research suggests supplementation may prevent tuberculosis or shorten the disease duration by strengthening the immune response [88, 89, 90].

A couple of studies also revealed that vitamin D supplementation, especially over the winter months, may protect children against the flu and respiratory infections. Stronger evidence for supplementation in adults is needed [91, 92, 93, 94, 95].

Additionally, people with HIV are often deficient in vitamin D, which can further weaken their immune response. Some evidence suggests supplementation can safely improve their immunity and vitamin D status [96, 97, 98, 99, 100, 101].

8) Supports Reproductive Health

Vitamin D deficiency during pregnancy can harm both the mother and the baby. It may lead to bone loss and osteomalacia in the mother. In newborns, it may cause impaired growth, bone, and enamel formation [102, 103, 104, 105, 106].

The recommended daily intake of vitamin D for children above 1 year old and adults up to 70 years old is 600 IU. The recommended intake stays the same for pregnant and breastfeeding women. Newborns and babies require at last 400 IU/day until 12 months [1].

Most experts consider vitamin D doses up to 4000 ID/day safe during pregnancy. Evidence is lacking to suggest supplementation can prevent pregnancy complications such as preterm birth and preeclampsia, though. Experts concluded that ongoing randomized clinical trials need to be completed to determine if vitamin D supplements (beyond that contained in prenatal vitamins) should be routinely recommended to pregnant women [107].

Vitamin D might also support men’s reproductive health and fertility. Limited studies suggest vitamin D may improve sperm motility [108, 109, 4, 110, 111, 112].

Data on the effects of vitamin D on fertility in women is sparse. Limited evidence suggests it may help women with PCOS, which impacts ovulation and fertility. Large-scale, clinical studies are needed (113, 114, 115, 116, 117).

At the recommended doses, vitamin D supports fertility and contributes to a healthy pregnancy. It also provides breastfed babies with vitamin D for bone development.

9) Good for the Hair & Skin

Vitamin D helps reduce inflammation in the body. Maintaining healthy levels might support skin and hair health.

Some scientists believe that people with skin problems like eczema, psoriasis, and hair loss need to be monitored to ensure they’re not deficient in vitamin D. More evidence is needed to support this practice [118].

According to limited studies, vitamin D shows promise for:

Nonetheless, hard evidence is lacking to support vitamin D supplementation in the majority of the cases. Topical creams may be beneficial in people with psoriasis when prescribed by a doctor.

Vitamin D Deficiency, Dosage & Supplementation

How to Maintain Normal Levels

Vitamin D levels can be increased and maintained by:

  • Regularly getting natural sunlight
  • Eating foods high in vitamin D
  • Supplementing

Most of the vitamin D3 in humans is derived from synthesis in the skin.

Very few foods in nature contain vitamin D. Major food sources are fatty fish (salmon, tuna, mackerel, sardines), cod liver oil, beef liver, egg yolks, cheese, and mushrooms (shiitake, portabella) [125].

Deficiency Prevalence

Vitamin D deficiency is fairly common in the United States, according to some estimates. It is defined as 25(OH)D blood levels of 20 ng/mL or below. Many factors can contribute to vitamin D deficiency. Some of them include inadequate sun exposure, gut disorders, liver disease, kidney disease, strict vegan diets, obesity, and certain medication [126, 127, 128].

Vitamin D deficiency may cause fatigue, back and bone pain, mood problems, and muscle weakness. Not all people with deficiency experience symptoms [129, 130, 131].

People who don’t get enough vitamin D through sunlight or dietary sources might need vitamin D supplements.

Supplement Types

Two forms of vitamin D exist: vitamin D2 and vitamin D3. Vitamin D2 (ergocalciferol) is mostly human-made and commonly added to foods.Vitamin D3 (cholecalciferol) is synthesized in the skin and found in animal-based foods [132].

Vitamin D3 is approximately 87% more effective in raising and maintaining the vitamin D levels in the body than vitamin D2. This form should be used for supplementation and fortification [133, 134, 135].

Since vitamin D fat-soluble and better absorbed when taken with fats. Bile salts help absorb vitamin D in the gut. Gut disorders, blocked bile flow, and bile-binding medications reduce vitamin D absorption [136, 137, 138].

Dosage

The recommended vitamin D doses are [139]:

  • For children up to 12 months old: 400 IU
  • For children and adults ages 1-70 years: 600 IU (including breastfeeding and pregnant women)
  • For people over 70 years old: 800 IU
Aim to get regular vitamin D from sun exposure and food to avoid deficiency. Adults up to 70 years old should get 600 IU/day.

Takeaway

Vitamin D is an essential fat-soluble vitamin produced by the skin during direct sunlight exposure. Some foods also contain small amounts of vitamin D. Most adults should aim to get 600 IU/day. Vitamin D plays important roles in the body. It helps build strong bones, balance the immune system, reduce inflammation, prevent infections, and maintain overall good health. Plus, it contributes to restful sleep and emotional balance, and it’s also a key prenatal vitamin. Studies have linked various health problems with vitamin D deficiency. However, strong evidence is lacking to support supplementation in most of the cases. This is probably because vitamin D deficiency is a result of inadequate sun exposure, which has many other negative health consequences aside from low vitamin D blood levels. Nonetheless, people who are deficient or at risk of deficiency may need to supplement to support bone health–particularly the elderly who have higher daily requirements, poor absorption, and reduced vitamin D production in the skin.

Further Reading

About the Author

Ana Aleksic

Ana Aleksic

MSc (Pharmacy)
Ana received her MS in Pharmacy from the University of Belgrade.
Ana has many years of experience in clinical research and health advising. She loves communicating science and empowering people to achieve their optimal health. Ana spent years working with patients who suffer from various mental health issues and chronic health problems. She is a strong advocate of integrating scientific knowledge and holistic medicine.

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