Winter is upon us and so is the risk of vitamin D deficiency and infections. Vitamin D, which is made in our skin following sunlight exposure and also found in oily fish (mackerel, tuna and sardines), mushrooms and fortified dairy and non-dairy substitutes, is essential for good health. Humans need vitamin D to keep healthy and to fight infections. The irony is that in winter, when people need vitamin D the most, most of us are not getting enough. So how much should we take? Should we take supplements? How do we get more? And, who needs it most?
I am a medical microbiologist and immunologist who studies the functions of vitamin D in immune cells. My laboratory has been interested in figuring out why the immune system has vitamin D receptors that determine which cells can use vitamin D. In the immune system, vitamin D acts to improve your ability to fight infections and to reduce inflammation.
The human body produces vitamin D as a response to sun exposure. A person can also boost their vitamin D intake through certain foods or supplements.
Vitamin D is essential for several reasons, including maintaining healthy bones and teeth. It may also protect against a range of diseases and conditions, such as type 1 diabetes.
Despite its name, vitamin D is not a vitamin, but a prohormone, or precursor of a hormone.
Vitamins are nutrients that the body cannot create, and so a person must consume them in the diet. However, the body can produce vitamin D.
In this article, we look at the benefits of vitamin D, what happens to the body when people do not get enough, and how to boost vitamin D intake.
Vitamin D has multiple roles in the body. It assists in:
- promoting healthy bones and teeth
- supporting immune, brain, and nervous system health
- regulating insulin levels and supporting diabetes management
- supporting lung function and cardiovascular health
- influencing the expression of genes involved in cancer development
Read on to find out about these roles in more detail:
- Healthy bones
Vitamin D plays a significant roleTrusted Source in the regulation of calcium and maintenance of phosphorus levels in the blood. These factors are vital for maintaining healthy bones.
People need vitamin D to allow the intestines to stimulate and absorb calcium and reclaim calcium that the kidneys would otherwise excrete.
Vitamin D deficiency in children can cause rickets, which leads to a severely bowlegged appearance due to the softening of the bones.
Similarly, in adults, vitamin D deficiency manifests as osteomalaciaTrusted Source, or softening of the bones. Osteomalacia results in poor bone density and muscular weakness.
A vitamin D deficiency can also present as osteoporosis, for which over 53 million people in the United States either seek treatment or face an increased risk.
- Reduced risk of flu
A 2018 reviewTrusted Source of existing research suggested that some studies had found that vitamin D had a protective effect against the influenza virus.
However, the authors also looked at other studies where vitamin D did not have this effect on flu and flu risk.
Further research is, therefore, necessary to confirm the protective effect of vitamin D on the flu.
- Healthy infants
Vitamin D deficiency has links to high blood pressure in children. One 2018 study found a possible connection between low vitamin D levels and stiffness in the arterial walls of children.
The American Academy of Allergy Asthma and Immunology (AAAAI) suggest that evidence points to a connection between low vitamin D exposure and an increased risk of allergic sensitization.
An example of this is children who live closer to the equator and have lower rates of admission to hospital for allergies plus fewer prescriptions of epinephrine autoinjectors. They are also less likely to have a peanut allergy.
The AAAAI also highlight an Australian study of egg intakeTrusted Source. Eggs are a common early source of vitamin D. The children who started eating eggs after 6 months were more likely to develop food allergies than children who started between 4–6 months of age.
Furthermore, vitamin D may enhance the anti-inflammatory effects of glucocorticoids. This benefit makes it potentially useful as a supportive therapyTrusted Source for people with steroid resistant asthma.
- Healthy pregnancy
A 2019 reviewTrusted Source suggests that pregnant women who are deficient in vitamin D may have a greater risk of developing preeclampsia and giving birth preterm.
Doctors also associate poor vitamin D status with gestational diabetes and bacterial vaginosis in pregnant women.
It is also important to note that in study shows , researchers associated high vitamin D levels during pregnancy with an increased risk of food allergy in the child during the first 2 years of life.
Although the body can create vitamin D, a deficiency can occur for many reasons.
Skin type: Darker skin, for example, and sunscreen, reduce the body’s ability to absorb the ultraviolet radiation B (UVB) rays from the sun. Absorbing sunlight is essential for the skin to produce vitamin D.
Sunscreen: A sunscreen with a sun protection factor (SPF) of 30 can reduce the body’s ability to synthesize the vitamin by 95% or moreTrusted Source. Covering the skin with clothing can inhibit vitamin D production also.
Geographical location: People who live in northern latitudes or areas of high pollution, work night shifts, or are homebound should aim to consume vitamin D from food sources whenever possible.
Breastfeeding: Infants who exclusively breastfeed need a vitamin D supplement, especially if they have dark skin or have minimal sun exposure.
Although people can take vitamin D supplements, it is best to obtain any vitamins or minerals.
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 complicationsTrusted Source, such as:
- cardiovascular conditions
- autoimmune problems
- neurological diseases
- pregnancy complications
- certain cancers, especially breast, prostate, and colon
Sources of vitamin D
Getting sufficient sunlight is the best way to help the body produce enough vitamin D. Plentiful food sources of vitamin D include:
- fatty fish, such as salmon, mackerel, and tuna
- egg yolks
- beef liver
- fortified milk
- fortified cereals and juices
The most common symptoms of excessive vitamin D include headache and nausea. However, too much vitamin D can also lead to the following:
- loss of appetite
- dry mouth
- a metallic taste
Excess vitamin D usually occurs from taking too many supplements. It is best to get vitamin D from natural sources.