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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It is undisputed that vitamin D plays a role everywhere in the body and performs important functions. A severe vitamin D deficiency, which can occur at a level of 12 nanograms per milliliter of blood or less, leads to severe and painful bone deformations known as rickets in infants and young children and osteomalacia in adults. Unfortunately, this is where the scientific consensus ends.
Where Does the Deficiency Begin?<p>Nobody knows exactly how much vitamin D a person actually needs. The question of when a deficiency starts is correspondingly controversial. However, vitamin D is becoming increasingly popular.Not only is the pseudo-scientific literature on the "sun vitamin" experiencing an upswing, but the number of published studies has also increased enormously in recent years. For example, in 2019 <a href="https://academic.oup.com/edrv/article/40/4/1109/5126915" target="_blank">a study found that</a> Vitamin D is responsible for keeping the skeleton functional and is associated with cardiovascular diseases, type 2 diabetes and various types of cancer. <br></p>
An All-Rounder<p>Vitamin D levels in the body rise and fall according to sun exposure. If sufficient UV rays reach the skin, the body is able to produce the vitamin itself. However, the human body only derives an estimated 10 to 20 percent of its daily requirement from food.</p><p>The vitamin D that we synthesize from sunlight or food is not biologically active at first. Before the kidneys can produce the biologically active form of the vitamin, known as calcitriol, and release it into the blood, some metabolic processes must take place beforehand.</p><p>In addition, many organs have receptors to which the precursor of calcitriol binds. Further, this substance is also present in blood.</p><p>From this precursor, the organs then produce calcitriol themselves, which the body then uses for countless other processes in the body. This form of vitamin D thus regulates insulin secretion, inhibits tumor growth, and promotes the formation of red blood cells as well as the survival and activity of macrophages, which are important for the <a href="https://www.mdpi.com/2072-6643/5/7/2502/htm" target="_blank">immune system.</a></p>
Low Vitamin D, Severe COVID-19 Disease?<p>A research study carried out <a href="https://www.sciencedirect.com/science/article/pii/S2352364620300067?via%3Dihub" target="_blank">at the University of Hohenheim</a> has now established a link between vitamin D deficiency, certain previous diseases, and severe cases of COVID-19.</p><p>According to the study, "there is a lot of evidence that several non-communicable diseases (high blood pressure, diabetes, cardiovascular diseases, metabolic syndrome) are associated with low vitamin D plasma levels. These comorbidities, together with the often accompanying vitamin D deficiency, increase the risk of severe COVID-19 events."</p><p>"This statement is completely correct," said Martin Fassnacht, head of endocrinology at the University Hospital of Würzburg. However, he qualifies that it is a pure association, "i.e. a mere observation that these events occur together.</p><p>Dr. Fassnacht is very critical of the hype surrounding vitamin D, but not because he denies the vitamin serves important functions. However, studies on humans have not been able to show that vitamin D has the healing powers many often propagate.</p><p>Fassnacht says, "If you take a closer look, the hopes that the administration of vitamin D has a healing effect have not been confirmed so far."</p>
Association Versus Intervention Studies<p>Many studies on the vitamin are association or observational studies. "By definition, these studies cannot prove the causal relationship, but only point to mere correlations," said Fassnacht. The physician tries to illustrate this with an example:</p><p>"Imagine two groups of 80-year-olds. One group is spry, active and does sports. If you compare them with another group living in nursing homes, the difference in vitamin D levels will be dramatic. Life expectancy would also be extremely different."</p><p>But to try to explain the difference in fitness by vitamin D status alone is far too simplistic. "Vitamin D levels are a good measure of how sick someone is. But not more," says Fassnacht. </p><p>According to Fassnacht, none of the intervention studies carried out to date -- that specifically examined the effect of vitamin D on various diseases -- has been able to confirm the previous association and laboratory studies or the presumed positive effect of vitamin D.</p>
Further Research Is Needed<p>"If a coronavirus infection is suspected, it is therefore absolutely necessary to check the vitamin D status and quickly correct any possible deficit," said the recommendation of the paper published by the University of Hohenheim.</p><p>"Studies are underway to see whether vitamin D helps in COVID-19 infection, but I personally do not believe that this is really the case," says endocrinologist Fassnacht. Nevertheless, he says it is of course useful to carry out these studies.<br></p><p>"I don't want to rule out that there are actually subgroups of people who benefit from an additional vitamin D dose," he says. After all, this has been proven to be the case with a severe deficit.</p><p>In view of the study situation, Fassnacht does not think much of preventive, nationwide vitamin D substitutes. "My belief that the vitamin helps somewhere is very low. But, of course, I can be wrong."</p>
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