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By Alina Petre

Vitamin D is a fat-soluble vitamin that is essential for optimal health.

Only a handful of foods contain significant amounts of this vitamin. These include fatty fish, organ meats, certain mushrooms and fortified foods.

However, unlike other vitamins that you can only get through your diet, vitamin D can also be made by your body when your skin is exposed to the sun.

For this reason, vitamin D is technically considered a hormone.

The limited availability of vitamin D in the human diet, combined with most people's insufficient sun exposure, may explain why up to 41.6 percent of the U.S. population has deficient blood levels (1).

Interestingly, having adequate blood levels of this vitamin can provide many important health benefits.

This article lists 15 science-based benefits linked to vitamin D.

1. Improves Bone Health

Vitamin D plays an important role in the health of your bones.

That's because it increases the absorption of calcium and phosphorus from your diet—two nutrients important for bone health.

Studies show that individuals with low blood levels tend to suffer from more bone loss (2).

In addition, research shows that individuals taking vitamin D supplements may benefit from a 23–33 percent lower risk of bone fractures (3, 4).

Moreover, recent studies report that taking vitamin D supplements may help improve fracture healing, especially in people with low levels. However, more studies are needed to support these results (5).

Most experts recommend that individuals with blood values under 12 ng/ml (25 nmol/l) should consider taking a vitamin D supplement that provides at least 20–25 mcg (800–1,000 IU) each day (2).

However, some insist that this recommendation is too low and propose that people take higher dosages in order to maintain blood vitamin D levels above 30 ng/ml (75 nmol/l) (6, 7, 8, 9).

In any case, all experts agree that elderly individuals, who have an elevated risk of falls and fractures, should supplement at the higher end of the recommendation (2).

Bottom Line: Vitamin D helps increase the absorption of minerals that are important for bone health. Higher levels may also reduce the risk of fractures, limit bone loss and improve recovery from fractures.

2. Reduces Diabetes Risk

Diabetes is a disorder in which your body cannot process carbs normally. Several types of diabetes exist, but type 1 and type 2 diabetes are the most common.

Type 1 diabetes is an autoimmune disease generally diagnosed during childhood or adolescence, whereas type 2 diabetes usually occurs later in life and is related to lifestyle.

Interestingly, vitamin D may help reduce the risk of both types of diabetes.

Type 1 Diabetes in Children

Type 1 diabetes is a genetic autoimmune disease that destroys the insulin-producing beta cells in the pancreas.

For this reason, type 1 diabetics must inject insulin several times per day to ensure their blood sugar stays at a healthy level (10).

Although type 1 diabetes has a large genetic component, certain environmental factors—perhaps including low vitamin D intake—may act together to promote the disease.

For instance, studies show that infants and toddlers who take vitamin D supplements may have a 29–88 percent lower risk of developing type 1 diabetes than infants given no supplements (11, 12).

The recommended daily allowance is 10 mcg (400 IU) vitamin D for infants 0–12 months and 15 mcg (600 IU) for most children and adults (13).

However, many argue that these recommendations are too low, with one study observing that only daily doses of 50 mcg (2,000 IU) and above successfully reduced the risk of developing type 1 diabetes (14).

That said, few studies have so far investigated the link between vitamin D and type 1 diabetes. More research is needed before strong conclusions can be made.

Type 2 Diabetes in Children, Teenagers and Adults

Type 2 diabetes is a disease that develops over time. It can happen if your pancreas stops producing enough insulin or if your body develops a resistance to insulin—or both (15).

Interestingly, vitamin D levels may play a role in the development of type 2 diabetes (16, 17, 18, 19).

Experts believe that vitamin D may protect against type 2 diabetes by reducing insulin resistance, increasing insulin sensitivity and enhancing the function of the cells responsible for producing insulin (17, 20, 21).

In fact, two recent reviews report that people with low blood vitamin D levels may have up to a 55 percent higher risk of developing type 2 diabetes (22, 23).

What's more, adults who consumed at least 12.5 mcg (500 IU) of vitamin D per day appeared to benefit from a 13 percent lower risk of developing type 2 diabetes than those who regularly consumed less than 5 mcg (200 IU) per day (23).

Similar results were also reported in vitamin-D-deficient children and teenagers with insulin resistance (24).

In another study, type 2 diabetics given 1,250 mcg (50,000 IU) vitamin D per week had a 5–21 percent decrease in fasting blood sugar levels and insulin resistance over the two-month study period, compared to controls (25).

It's important to mention that not all reviews agree on the protective effects of taking vitamin D supplements (26, 27, 28).

Although it is possible that not all type 2 diabetics benefit from taking vitamin D supplements, it seems particularly beneficial to those with poor blood sugar control (26).

Bottom Line: Adequate vitamin D levels may help reduce the risk of developing both type 1 and type 2 diabetes. In certain cases, vitamin D supplements may also help improve blood sugar control in type 2 diabetics.

3. Could Improve Heart Health

Vitamin D may help improve the health of your heart and reduce the likelihood of heart attacks.

In one study, men with blood levels below 15 ng/ml (37 nmol/l) were twice as likely to get a heart attack as those with levels of 30 ng/ml (75 nmol/l) or higher (29).

In another study, the likelihood of developing heart disease was 153 percent higher for people with blood vitamin D levels below 15 ng/ml (37 nmol/l) (30).

The highest risk was seen in individuals with low vitamin D levels who also had high blood pressure (30).

That said, although low blood vitamin D levels are often linked to an increased risk of heart disease, many studies fail to find a decreased risk from taking vitamin D supplements (31, 32, 33, 34).

Experts speculate that other factors linked to a good vitamin D status may be at play, such as time spent outdoors or a preference for vitamin-D-fortified beverages instead of soft drinks (35).

Thus, although taking vitamin D supplements may be beneficial for other reasons, increasing your levels through lifestyle choices still seems to be the best strategy against heart disease.

Bottom Line: Individuals with a good vitamin D status have a lower risk of developing heart disease. However, taking supplements doesn't seem to have an effect.

4. May Lower Your Risk of Certain Cancers

Maintaining adequate vitamin D levels may have some benefits for preventing cancer.

In fact, various studies suggest that individuals with higher levels have a lower risk of certain types of cancer (36, 37).

Two recent reviews report that those with adequate levels may have up to a 25 percent lower risk of developing bladder cancer. Higher vitamin D levels may also reduce the risk of dying from the disease (38, 39).

Similarly, several other studies show that maintaining higher blood vitamin D levels may reduce the risk of developing colorectal cancer (40, 41, 42, 43).

In addition, some studies report that vitamin D may play a role in slowing down the progression of cancer. That said, it remains unclear whether taking vitamin D supplements provides any anti-cancer benefits (44).

In fact, several studies failed to find protective effects against cancer after participants took vitamin D supplements, despite having increased blood levels (45, 46, 47, 48, 49).

In sum, more studies are needed to determine cause and effect, as well as the true value of taking vitamin D supplements as an anti-cancer strategy.

Until then, it may be wise to focus on maintaining adequate vitamin D levels through lifestyle choices that are known to reduce the risk of cancer. For instance, through a healthy diet and regular physical activity—preferably outdoors.

Bottom Line: Vitamin D may play a role in cancer prevention. However, more studies are needed to determine its exact role.

By Franziska Spritzler

Vitamin D is an extremely important vitamin that has powerful effects on several systems throughout the body (1).

Unlike most vitamins, vitamin D actually functions like a hormone and every single cell in your body has a receptor for it.

Your body makes it from cholesterol when your skin is exposed to sunlight.

Vitamin D is an extremely important vitamin that has powerful effects on several systems throughout the body.iStock

It's also found in certain foods such as fatty fish and fortified dairy products, although it's very difficult to get enough from diet alone.

The recommended daily intake is usually around 400-800 IU, but many experts say you should get even more than that.

Vitamin D deficiency is very common. It's estimated that about 1 billion people worldwide have low levels of the vitamin in their blood (2).

According to a 2011 study, 41.6 percent of adults in the U.S. are deficient. This number goes up to 69.2 percent in Hispanics and 82.1 percent in African-Americans (3).

These are common risk factors for vitamin D deficiency:

  • Having dark skin.
  • Being elderly.
  • Being overweight or obese.
  • Not eating much fish or milk.
  • Living far from the equator where there is little sun year-round.
  • Always using sunscreen when going out.
  • Staying indoors.

People who live near the equator and get frequent sun exposure are less likely to be deficient, because their skin produces enough vitamin D to satisfy the body's needs.

Most people don't realize that they are deficient, because the symptoms are generally subtle. You may not notice them easily, even if they are having a significant negative effect on your quality of life.

Here are eight signs and symptoms of vitamin D deficiency.

1. Getting Sick or Infected Often

One of vitamin D's most important roles is keeping your immune system strong so you're able to fight off the viruses and bacteria that cause illness.

It directly interacts with the cells that are responsible for fighting infection (4).

If you become sick often, especially with colds or the flu, low vitamin D levels may be a contributing factor.

Several large observational studies have shown a link between a deficiency and respiratory tract infections like colds, bronchitis and pneumonia (5, 6).

A number of studies have found that taking vitamin D supplements at dosages of up to 4,000 IU daily may reduce the risk of respiratory tract infections (7, 8, 9).

In one study of people with the chronic lung disorder COPD, only those who were severely deficient in vitamin D experienced a significant benefit after taking a high-dose supplement for one year (10).

Bottom Line: Vitamin D plays important roles in immune function. One of the most common symptoms of deficiency is an increased risk of illness or infections.

2. Fatigue and Tiredness

Feeling tired can have many causes and vitamin D deficiency may be one of them.

Unfortunately, it's often overlooked as a potential cause.

Case studies have shown that very low blood levels can cause fatigue that has a severe negative effect on quality of life (11, 12).

In one case, a woman who complained of chronic daytime fatigue and headaches was found to have a blood level of only 5.9 ng/ml. This is extremely low, as anything under 20 ng/ml is considered to be deficient.

When the woman took a vitamin D supplement, her level increased to 39 ng/ml and her symptoms resolved (12).

However, even blood levels that aren't extremely low may have a negative impact on energy levels.

A large observational study looked at the relationship between vitamin D and fatigue in young women.

The study found that women with blood levels under 20 ng/ml or 21–29 ng/ml were more likely to complain of fatigue than those with blood levels over 30 ng/ml (13).

Another observational study of female nurses found a strong connection between low vitamin D levels and self-reported fatigue.

What's more, the researchers found that 89 percent of the nurses were deficient (14).

Bottom Line: Excessive fatigue and tiredness may be a sign of vitamin D deficiency. Taking supplements may help improve energy levels.

3. Bone and Back Pain

Vitamin D is involved in maintaining bone health through a number of mechanisms.

For one, it improves your body's absorption of calcium.

Bone pain and lower back pain may be signs of inadequate vitamin D levels in the blood.

Large observational studies have found a relationship between a deficiency and chronic lower back pain (15, 16, 17).

One study examined the association between vitamin D levels and back pain in more than 9,000 older women.

The researchers found that those with a deficiency were more likely to have back pain, including severe back pain that limited their daily activities (17).

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 (18).

Bottom Line: Low blood levels of the vitamin may be a cause or contributing factor to bone pain and lower back pain.

4. Depression

A depressed mood may also be a sign of deficiency.

In review studies, researchers have linked vitamin D deficiency to depression, particularly in older adults (19, 20).

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

On the other hand, most of the controlled trials, which carry more scientific weight than observational studies, didn't show a link between the two (19).

However, the researchers who analyzed the studies noted that the dosages of vitamin D in controlled studies were often very low.

In addition, they noted that some of the studies may not have lasted long enough to see the effect of taking supplements on mood.

Some controlled studies have shown that giving vitamin D to people who are deficient helps improve depression, including seasonal depression that occurs during the colder months (21, 22).

Bottom Line: Depression is associated with low vitamin D levels and some studies have found that supplementing improves mood.

5. Impaired Wound Healing

Slow healing of wounds after surgery or injury may be a sign that vitamin D levels are too low.

Results from a test-tube study suggest that the vitamin increases production of compounds that are crucial for forming new skin as part of the wound-healing process (23).

One study on patients who had dental surgery found that certain aspects of healing were compromised by vitamin D deficiency (24).

It's also been suggested that vitamin D's role in controlling inflammation and fighting infection is important for proper healing.

One analysis looked at patients with diabetic foot infections.

It found that those with severe vitamin D deficiency were more likely to have higher levels of inflammatory markers that can jeopardize healing (25).

Unfortunately, at this point there is very little research about the effects of vitamin D supplements on wound healing in people with deficiency.

However, one study found that when vitamin D deficient patients with leg ulcers were treated with the vitamin, ulcer size reduced by 28 percent, on average (26).

Bottom Line: Inadequate vitamin D levels may lead to poor wound healing following surgery, injury or infection.

6. Bone Loss

Vitamin D plays a crucial role in calcium absorption and bone metabolism.

Many older women who are diagnosed with bone loss believe they need to take more calcium. However, they may be deficient in vitamin D as well.

Low bone mineral density is an indication that calcium and other minerals have been lost from bone. This places older people, especially women, at an increased risk of fractures.

In a large observational study of more than 1,100 middle-aged women in menopause or postmenopause, researchers found a strong link between low vitamin D levels and low bone mineral density (27).

However, a controlled study found that women who were vitamin D deficient experienced no improvement in bone mineral density when they took high-dose supplements, even if their blood levels improved (28).

Regardless of these findings, adequate vitamin D intake and maintaining blood levels within the optimal range may be a good strategy for protecting bone mass and reducing fracture risk.

Bottom Line: A diagnosis of low bone mineral density may be a sign of vitamin D deficiency. Getting enough of this vitamin is important for preserving bone mass as you get older.

7. Hair Loss

Hair loss is often attributed to stress, which is certainly a common cause.

However, when hair loss is severe, it may be the result of a disease or nutrient deficiency.

Hair loss in women has been linked to low vitamin D levels, although there is very little research on this so far (29).

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 (30).

Low vitamin D levels are linked to alopecia areata and may be a risk factor for developing the disease (31, 32, 33).

One study in people with alopecia areata showed that lower blood levels tended to be associated with a more severe hair loss (33).

In a case study, topical application of a synthetic form of the vitamin was found to successfully treat hair loss in a young boy with a defect in the vitamin D receptor (34).

Bottom Line: Hair loss may be a sign of vitamin D deficiency in female-pattern hair loss or the autoimmune condition alopecia areata.

8. Muscle Pain

The causes of muscle pain are often difficult to pinpoint.

There is some evidence that vitamin D deficiency may be a potential cause of muscle pain in children and adults (35, 36, 37).

In one study, 71 percent of people with chronic pain were found to be deficient (37).

The vitamin D receptor is present in nerve cells called nociceptors, which sense pain.

One study in rats showed that a deficiency led to pain and sensitivity due to stimulation of nociceptors in muscles (38).

A few studies have found that taking high-dose vitamin D supplements may reduce various types of pain in people who are deficient (39, 40).

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 of 57 percent (40).

Bottom Line: There is a link between chronic pain and low blood levels of the vitamin, which may be due to the interaction between the vitamin and pain-sensing nerve cells.

Correcting a Vitamin D Deficiency is Simple

Vitamin D deficiency is incredibly common and most people are unaware of it.

That's because the symptoms are often subtle and non-specific, meaning that it's hard to know if they're caused by low vitamin D levels or something else.

If you think you may have a deficiency, then it's important that you speak to your doctor and get your blood levels measured.

Fortunately, a vitamin D deficiency is usually easy to fix. You can either increase your sun exposure, eat more vitamin D rich foods or simply take a supplement.

Fixing your deficiency is simple, easy and can have big benefits for your health.

Reposted with permission from our media associate Authority Nutrition.

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