As a response to sun exposure a human body produces vitamin D. A person can also increase his or her intake of vitamin D through certain foods or supplements.
For several reasons, vitamin D is important including the preservation of healthy bones and teeth. It may also defend against a range of conditions and diseases such as type 1 diabetes.
Vitamin D is not a vitamin, despite its name but a prohormone, or a precursor to a hormone.
Vitamins are nutrients the body can’t create, so a person needs to eat them in the diet. Yet vitamin D can be provided by the body.
In this post, we look at the benefits of vitamin D, what happens to the body when people are not getting enough, and how vitamin D intake can be improved.
Vitamin D plays many functions in the body. It assists in:
- promoting healthy bones and teeth
- supporting the health of the body brain and nervous system
- controlling insulin levels and supporting the treatment of diabetes
- supporting lung function and cardiovascular health
- influencing the expression of genes involved in the development of cancer.
Read more about these roles below:
1. Healthy bones
Vitamin D plays an important role in controlling calcium and in maintaining levels of phosphorus in the blood. These factors are vital to keeping bones healthy.
People need vitamin D to stimulate and absorb calcium in the intestines, and to reclaim calcium that would otherwise be excreted by the kidneys.
Children’s vitamin D deficiency can cause rickets, leading to a severe bowlegged appearance due to bone softening.
Similarly, vitamin D deficiency in adults is manifested as osteomalacia, or bone softening. Osteomalacia results in poor muscle weakness and bone density.
A deficiency in vitamin D can also occur as osteoporosis, for which more than 53 million people in the United States either seek treatment or face increased risk.
2. Reduced risk of contracting flu
A analysis of existing research in 2018 indicated that some studies had found vitamin D to have a protective effect against the influenza virus.
However, the authors have checked other studies in which vitamin D did not have this effect on the prevention of pneumonia and flu.
Therefore more research is needed to confirm the protective effect of vitamin D on the flu.
3. Healthy infants
Deficiency of vitamin D has associations with high blood pressure in infants. One 2018 report found a possible correlation between low levels of vitamin D and stiffness in children’s arterial walls.
The American Academy of Allergy Asthma and Immunology (AAAAI) indicates evidence points to a correlation between low exposure to vitamin D and increased risk of allergic sensitization.
Another example of this is children living closer to the equator and having lower hospital admission levels for asthma and less epinephrine autoinjector prescriptions. You also have less chance of having peanut allergy.
The AAAAI also highlight an Australian egg intake survey. Eggs are a growing source of Vitamin D early in life. The children who started eating eggs after 6 months were more likely to develop food allergies than those who started between the ages of 4–6 months.
In addition, glucocorticoids can improve the anti-inflammatory effects of vitamin D. It advantage makes it potentially useful for people with steroid resistant asthma as a supportive therapy.
4. Healthy pregnancy
A 2019 review suggests that pregnant women with a vitamin D deficiency may have a higher risk of developing preeclampsia and giving preterm birth.
Physicians of pregnant women often link low status of vitamin D with gestational diabetes and bacterial vaginosis.
It is also important to note that researchers in a 2013 study correlated high levels of vitamin D during pregnancy with an increased risk of food allergy in the infant over the first 2 years of life.
While vitamin D may be produced by the body, a deficiency can occur for many reasons.
Body type: For example, darker skin and sunscreen decrease the ability of the body to absorb ultraviolet rays B (UVB) from the sun. Absorbing sunlight is essential to producing vitamin D for the skin.
Sunscreen: A sunscreen of 30 with a sun protection factor (SPF) can reduce the ability of the body to synthesize the vitamin by 95 percent or more. Clothing covering the skin can hinder the production of vitamin D, too.
Geographical location: People who live in high-pollution areas or northern latitudes, work night shifts, or are homebound will try to eat vitamin D from food sources where possible.
Breastfeeding: Babies who only breastfeed need a vitamin D supplement, particularly if they have dark skin or insufficient exposure to sunlight. The American Academy of Pediatrics recommends providing 400 international units (IU) of oral vitamin D per day for all breastfed infants.
While people can take supplements with vitamin D, it is better to get any vitamins or minerals from natural sources wherever possible.
Symptoms of vitamin D deficiency may include:
- regular sickness or infection
- bone and back pain
- low mood
- impaired wound healing
- hair loss
- muscle pain
If Vitamin D deficiency continues for long periods, it may result in complications, such as:
- cardiovascular conditions
- autoimmune problems
- neurological diseases
- pregnancy complications
- certain cancers, especially breast, prostate, and colon.
Sources of vitamin D
The best way to help the body produce enough vitamin D is by getting enough sunlight. Plenty of vitamin D-food sources include:
- fatty fish, such as salmon, mackerel, and tuna
- egg yolks
- beef liver
- fortified milk
- fortified cereals and juices
People can measure intake of vitamin D in micrograms (mcg) or in international units (IU). One microgram of vitamin D stands at 40 IU.
The recommended daily intakes of vitamin D are as follows:
- Infants 0–12 months: 400 IU (10 mcg).
- Children 1–18 years: 600 IU (15 mcg).
- Adults up to 70 years: 600 IU (15 mcg).
- Adults over 70 years: 800 IU (20 mcg).
- Pregnant or lactating women: 600 IU (15 mcg).
Sensitive exposure to sun on bare skin for 5–10 minutes, 2–3 days a week, helps the majority of people to generate enough vitamin D. Vitamin D breaks down quite quickly, however, which means stores can run low, particularly in wintertime.
For an adult the upper limit recommended by healthcare professionals for vitamin D is 4,000 IU per day. The National Institutes of Health (NIH) report, however, that toxicity with vitamin D is impossible at intakes below 10,000 IU per day.
Excessive vitamin D intake can lead to excessive calcification of bones and hardening of blood vessels, liver, lung and heart tissues.
Headache and nausea represent the most common symptoms of excessive vitamin D. But too much vitamin D could also lead to the following:
- loss of appetite
- dry mouth
- a metallic taste
Normally, excess vitamin D comes from taking too many supplements. Vitamin D is better derived from natural sources.
If someone is taking supplements, they should carefully select their brand, as the FDA is not checking vitamin health or purity.
It is the total diet and eating pattern that is most important for the prevention and good health of diseases. Eating a diet with a range of nutrients is safer than focussing on one food as the answer to good health.
Is sunlight exposure worth the skin cancer risk to make sure people get enough vitamin D?
It does seem like 10–15 minutes of sun exposure a few times a week is harmless, but that exposure can have consequences over your lifetime.
As little as 60 seconds of UVA exposure to the sun can increase your risk for melanoma. You are likely to get enough vitamin D through food, and increasing your intake of vitamin D through sun exposure is not worth the added risk.
If you are not getting enough, then seek out supplements. Experts also recommend that if you will be going outside, you apply sunscreen every 2 hours with a good, broad spectrum sunscreen of SPF 15 or higher. A useful resource for this type of information is skincancer.org.
Debra Sullivan, PhD, MSN, RN, CNE, COI
Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.