According to the Centers for Disease Control and Protection (CDC), about a quarter of the population is at risk for vitamin D "inadequacy." A simple blood test can detect if this becomes vitamin D deficiency.
Testing for a deficiency is now considered to be part of blood work that is done yearly. This article explores how to detect and treat the signs of vitamin D deficiency.
What is vitamin D?
Vitamin D is a fat-soluble vitamin that is made when the skin is exposed to sunlight. It is present in only a small number of foods, including fortified products, such as milk.
Vitamin D is best known for supporting calcium metabolism. It helps the body absorb calcium from food and supplements to support the maintenance of healthy bones cells.
But working with calcium to protect the bones is far from the only function of vitamin D in the body.
Vitamin D comes from a small variety of foods and is produced when the skin is exposed to sunlight.
Vitamin D also:
- supports muscle health
- plays a role in the immune system
- aids cell growth
- reduces inflammation, which can lead to illness such as rheumatoid arthritis and cancer
- regulates blood pressure and supports cardiovascular health
Vitamin D intake is not the best measure of the vitamin's status in the body, as many factors can affect its uptake. For example, the health of the stomach can interfere with how much vitamin D a person absorbs from the food they eat.
What causes vitamin D deficiency?
People with serum vitamin D levels of less than 20 nanograms/milliliter (ng/mL) are at risk for vitamin D deficiency.
Serum levels below 12 ng/mL indicate there is a vitamin D deficiency.
Vitamin D deficiency occurs when a person either does not consume enough vitamin D or when their body cannot absorb and metabolize the vitamin D they do consume.
Below are some of the factors that affect whether or not a person is at risk of having a deficiency:
- Living at a high latitude: This is due to there being less access to the sun's ultraviolet-B (UVB) rays.
- Being indoors too much: Spending little or no time outside means missing out on the sun's rays.
- Living in a highly polluted area: Pollution can absorb some of the sun's rays, so reducing scope to make vitamin D.
- Using large quantities of sunscreen: Using enough sunscreen to block UV rays might inhibit vitamin D absorption. But few people use enough sunscreen to block UV rays fully.
- Having darker skin: People with darker skin need more sunlight exposure to absorb enough vitamin D.
- Ambient temperature: Warm skin is better at absorbing the sun's rays to produce vitamin D than cool or cold skin.
- Diet: Eating foods rich in vitamin D, or foods that have been fortified with the vitamin, reduces the risk of vitamin D deficiency.
- Being overweight: Research suggests that being overweight correlates with lower vitamin D levels. This may be because excess body fat somehow affects vitamin D absorption.
- Age: People's ability to absorb vitamin D may decline with increasing age.
- Gut health: Disorders that affect the gut, such as Crohn's disease, can undermine the intestines' ability to absorb vitamin D.
- Kidney and liver health: People with liver or kidney disease tend to have lower vitamin D levels.
- Pregnancy or breast-feeding: The nutritional demands of an infant or fetus may lower vitamin D levels, particularly in women already at risk of vitamin D deficiency.
- Being a breast-feeding infant: Human milk is low in vitamin D. Infants who are nursing may need a vitamin D supplement, particularly if they do not go outdoors everyday.
A vitamin D deficiency can cause exhaustion and changes in mood.
Many people with a vitamin D deficiency may have no symptoms or may go many years without experiencing symptoms.
The symptoms of vitamin D deficiency can be vague, may change over time, and are similar to symptoms of a wide range of ailments. Hence, it is dangerous to self-diagnose a vitamin D deficiency.
People who experience symptoms of vitamin D deficiency, or who have unexplained illnesses or nutritional deficiencies, should request a test for vitamin D deficiency. Some symptoms of a deficit in vitamin D include:
- thinning or brittle bones, osteoporosis, or frequent bone fractures
- muscle weakness, particularly if there is an unexplained change in muscle strength
- changes in mood, with people who have low vitamin D experiencing anxiety or depression
- chronic pain, as vitamin D plays a key role in supporting bone, muscle, and cell health
- high or rising blood pressure
- exhaustion, even with enough sleep
- decreased endurance
- unexplained infertility
There is disagreement about the right amount of vitamin D for good health. Ideal vitamin D intake varies with different factors, such as age, activity level, and metabolic health. People should talk to a doctor about vitamin D intake goals.
It is a good idea to keep a log of symptoms when treatment begins. This is a simple way to track progress, and to assess whether it is necessary to increase vitamin D intake.
There are three strategies for increasing vitamin D levels:
- Take a vitamin D supplement: These are readily available over the counter. A doctor may also prescribe a supplement or multivitamin. For most adults, the recommended dietary allowance (RDA) is 600 IU. For adults over 70, the RDA is 800 IU. For children under 12 months, it is 400 IU.
- Eat foods rich in vitamin D: Fatty fish such as tuna, salmon, and mackerel, as well as fish liver oils, are excellent natural sources. Beef liver, cheese, and egg yolks contain small quantities of vitamin D. Milk is fortified with vitamin D, as are many cereals.
- Increase exposure to natural sunlight: The risks of sun exposure might be greater than the risks of vitamin D deficiency for people vulnerable to sunburn, with a history of skin cancer, or with very pale skin. They should talk to a doctor about whether spending more time in natural light is a good idea or not.
Preventing vitamin D deficiency
Eating foods rich in vitamin D and spending 15-20 minutes each day in natural sunlight are the best strategies for preventing vitamin D deficiency.
Spending time outdoors in natural sunlight each day can help prevent a vitamin D deficiency.
Depending upon vitamin D intake goals and a person's health, a vitamin D supplement may also help. It is best to talk to a doctor before taking a supplement.
Some other lifestyle strategies that may support healthy vitamin D levels include:
- Maintain a healthy body weight: Try taking walks outside to get daily exercise and exposure to sunlight.
- Monitoring and treating medical conditions: This especially applies to those that effect gut, liver, and kidney health.
- Using vitamin D supplements: Particularly for infants who are being breast-fed.
- Talking to a doctor about any changes in health: Particularly if there is a family history of osteoporosis or vitamin D deficiency.