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 nondairy 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?
Where to Get Your Vitamin D<p>Vitamin D is called the sunshine vitamin since it is made in the skin after exposure to sun. The same UVB rays that cause a sunburn also make vitamin D. Sunscreen, darker skin pigmentation, clothing and reduced daylight in winter diminish the skin's ability to make vitamin D. The people who experience the biggest seasonal swings in vitamin D levels are fair-skinned individuals <a href="https://doi.org/10.3390/nu10040457" target="_blank">living in the northern regions</a> of the U.S. and at <a href="https://doi.org/10.3945/an.117.015578" target="_blank">higher latitudes around the globe</a> where there is very little daylight in winter.</p><p>But those most at risk for low vitamin D levels are people of color and people living at higher latitudes. Dark-skinned individuals are more likely than fair-skinned individuals to be low for vitamin D year-round because the darker skin blocks the UVB rays from producing vitamin D. However, even in dark skinned individuals, vitamin D is lowest in the winter.</p><p>In the winter, in addition to high vitamin D food, adults should take additional vitamin D from foods and/or supplements to <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#en1" target="_blank">get at least 600 IU per day of vitamin D.</a> People who have dark skin or avoid sunshine should eat more vitamin D year-round.</p>
Vitamin D's Importance for Bones and Microbes<p>Originally, doctors thought that vitamin D was only important for bone health. This was because the vitamin D deficiency caused bone diseases like <a href="http://doi.org/10.1172/JCI29449" target="_blank">rickets in children and osteoporosis in adults</a>. However, in the 1980s scientists discovered that <a href="https://www.jci.org/articles/view/111557" target="_blank">immune cells</a> <a href="https://science.sciencemag.org/content/224/4656/1438" target="_blank">had receptors for vitamin D</a>.</p><p>My group's research has shown that vitamin D plays an important role in <a href="https://doi.org/10.1080/10409238.2019.1611734" target="_blank">maintaining health in the gastrointestinal tract</a>. <a href="https://iai.asm.org/content/84/11/3094" target="_blank">Higher levels of vitamin D</a> reduce <a href="https://doi.org/10.1016/j.tem.2019.04.005" target="_blank">susceptibility to inflammatory bowel disease</a> and <a href="http://doi.org/10.1038/ajg.2016.53" target="_blank">Crohn's disease</a>, <a href="https://doi.org/10.3389/fimmu.2019.00001" target="_blank">gut</a> and <a href="http://doi.org/10.1128/IAI.00679-16" target="_blank">lung infections</a> in animals and people.</p><p>My colleagues and I have discovered that one of the ways vitamin D functions is by keeping the microbes in the gut healthy and happy. Vitamin D <a href="https://doi.org/10.1177/1535370214523890" target="_blank">increases the number and diversity of microbes</a> living in the gut, which together reduce inflammation throughout the body.</p><p>Low vitamin D levels are <a href="https://doi.org/10.1038/nrgastro.2015.34" target="_blank">associated with inflammatory bowel disease</a> in humans. Researchers have found that <a href="https://doi.org/10.1007%2Fs00535-017-1313-6" target="_blank">inflammatory bowel disease patients in Japan</a> have more symptoms in winter than during other seasons.</p>
Why is vitamin D more important in winter?<p>In the winter, humans are exposed to more infections and spend less time outside. Exactly how much vitamin D healthy adults should have is debated. Some authorities recommend from <a href="https://www.nature.com/articles/nrendo.2017.31" target="_blank">200 IU per day to 2,000 IU per day</a>. In the U.S., the <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" target="_blank">Institutes of Medicine</a> recommends 600-800 IU per day for adults, while the <a href="https://doi.org/10.1210/jcem.96.12.zeg3908" target="_blank">Endocrine Society states that optimal vitamin D status</a> may require 1500-2,000 IU per day. In the winter, people have a reduced ability to make vitamin D when they go outside, so amounts of at least 600 IU per day of vitamin D from food or supplements would help maintain vitamin D status at summer levels.</p><p>But, just like many things, <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" target="_blank">too much vitamin D can be harmful</a>. Vitamin D toxicity does not result from too much sun or food. Because of the risk of skin cancer, dermatologists and other health professionals do not recommend unprotected sun exposure to boost your vitamin D. Instead they suggest supplements. But vitamin D toxicity can occur if an individual takes too many.</p><p>The experts that set the national intakes of vitamin D for the U.S. recommend that adult individuals take <a href="https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/" target="_blank">no more than 4,000 IU per day of vitamin D</a> to avoid toxic side effects. Vitamin D helps you absorb calcium from your diet, but when vitamin D is too high, calcium levels in the blood go up and that can lead to kidney disease.</p><p>By consuming more vitamin D during the winter your gut microbes will be healthier and you'll be more resistant to infection and inflammation year-round.</p>
EcoWatch Daily Newsletter
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).
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).
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.
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.
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).
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).
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).
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).
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.
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).
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 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.
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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.
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.
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.
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.
A depressed mood may also be a sign of deficiency.
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.
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).
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.
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).
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.