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Unlike other vitamins, vitamin D functions like a hormone, and every single cell in your body has a receptor for it.  Known as the sunshine vitamin it is produced by the body in response to skin being exposed to sunlight. It is also occurs naturally in a few foods — including some fish, fish liver oils and egg yolks.

Vitamin D is very important for health. Some of its roles in the body include:


  • helping with the absorption of calcium
  • maintaining healthy bones
  • regulating genes and cell growth
  • preventing rickets and osteoporosis
  • modulating the immune system


The recommended daily intake (RDI) is around 500–800 IU, but experts say you should get even more than that. Vitamin D deficiency is very common nowadays. About 1 billion people worldwide have low levels of the vitamin in their blood.

According to a 2011 study, 41.6% of adults in the US are deficient. This number goes up to 69.2% in Hispanics and 82.1% in African-Americans. Here are common risk factors for vitamin D deficiency:


  • Dark skin.
  • Being elderly.
  • Being overweight or obese.
  • Not eating much fish or dairy.
  • Living far from the equator where there is little sun year-round.
  • Always using sunscreen when going out.
  • Staying indoors.
  • If kidneys or liver cannot convert vitamin D to its active form.
  • Breastfed infants. Human milk is a poor source of vitamin D. If you are breastfeeding, give your infant a supplement of 400 IU of vitamin D every day.
  • People with disorders such as Crohn’s disease or celiac disease who don’t handle fat properly, because vitamin D needs fat to be absorbed.
  • Air Pollution
  • Smoking


The most accurate way to measure how much vitamin D is in your body is the 25-hydroxy vitamin D blood test. A level of 20 nanograms/milliliter to 50 ng/mL is considered normal for healthy people. A level less than 12 ng/mL indicates vitamin D deficiency. Here are signs and symptoms of vitamin D deficiency.


  1. Getting Sick Often


One of vitamin D’s most important roles is keeping your immune system strong. It interacts with the cells that are responsible for fighting infection.  If you have vitamin D deficiency you can often become sick, especially with colds or the flu.

Maintaining adequate vitamin D levels could lessen the length and severity of respiratory infections and possibly even prevent them from occurring. A review of 12 studies, including 2,279 children, found that children with respiratory infections had significantly lower vitamin D levels compared with controls.


  1. Bone and Back Pain


Vitamin D enhances the absorption of dietary calcium by 30%-40% and phosphorus by 80%. Vitamin D insufficiency leads to secondary hyperparathyroidism that causes osteopenia, osteomalacia and osteoporosis.

Bone pain and lower back pain may be signs of low vitamin D. Large observational studies have found a relationship between a deficiency and chronic lower back pain. In one controlled study, people with vitamin D deficiency were nearly twice as likely to experience bone pain in their legs, ribs or joints compared to those with blood levels in the normal range.


  1. Depression


A depressed mood may also be a sign of vitamin D deficiency.

In one analysis, 65% of the observational studies found a relationship between low blood levels and depression.

Some controlled studies have shown that giving vitamin D to people who are deficient helps improve seasonal depression. The researchers believe that because vitamin D is important to healthy brain function, insufficient nutrient levels may play a role in depression and other mental illnesses.

Another review of 13 studies with over 31,000 participants found that those with a vitamin D deficiency had an increased risk for depression, when compared to those with higher levels of Vitamin D.

Low Vitamin D levels may impair cognitive function because there are vitamin D receptors in areas of the brain that are responsible for mood and behavior, including the development of depression.

However, research hasn’t proven that getting more vitamin D is a sufficient treatment for depression.


  1. Hair Loss


When hair loss is severe, it may be the result of a disease or nutrient deficiency.  Vitamin D plays a role in stimulating new and old hair follicles. When there isn’t enough vitamin D in your system, new hair growth can be stunted. Another important function of vitamin D is to help regulate cell cycles, which is particularly important when it comes to hair growth. In patients with alopecia areata, for example, research seems to show that hair follicle cycling is disrupted due to low levels of vitamin D.

Alopecia areata is an autoimmune disease characterized by severe hair loss from the head and other parts of the body. It’s associated with rickets, which is a disease that causes soft bones in children due to vitamin D deficiency.

Low vitamin D levels are linked to alopecia areata and may be a risk factor for developing the disease.


  1. Muscle pain


Vitamin D deficiency is suspiciously common in people with chronic pain, maybe because it actually causes it or at least makes it worse. Vitamin D actually has plenty to do with muscle, both muscle pain and weakness.

In one study, 71% of people with chronic pain were found to be deficient. The vitamin D receptor is present in nerve cells called nociceptors, which sense pain. Another study with rats showed that a deficiency led to pain and sensitivity due to stimulation of nociceptors in muscles.

Also few studies have found that taking high-dose vitamin D supplements may reduce various types of pain in people who are deficient. One study in 120 children with vitamin D deficiency who had growing pains found that a single dose of the vitamin reduced pain scores by an average 57%.

Muscle spasms (tetany) may be the first sign of rickets in infants. They are caused by a low calcium level in the blood in people with severe vitamin D deficiency.

Vitamin D deficiency is very common and most people are unaware of it. That’s because the symptoms are often subtle and non-specific and it is hard to know if they’re caused by low vitamin D levels or something else.

Fortunately, a vitamin D deficiency is usually easy to fix. You can either increase your sun exposure or take vitamin D supplements.