Vitamin D - Why Vitamin D is important to our Body?

Vitamin D is both a nutrient we eat and a hormone our bodies make. It is a fat-soluble vitamin that has long been known to help the body absorb and store calcium and phosphorus, both of which are important for bone formation. In addition, laboratory studies show that vitamin D can reduce the growth of cancer cells, fight infections and inhibit inflammation. Many organs and tissues in the body have receptors for vitamin D, suggesting important functions beyond bone health, and scientists are actively investigating other possible functions.

Few foods naturally contain vitamin D, although some foods are fortified with it. For most people, taking supplements is the best way to get enough vitamin D because it is difficult to get enough from food. Vitamin D supplements are available in two forms: vitamin D2 ("ergocalciferol" or pre-vitamin D) and vitamin D3 ("cholecalciferol"). Both are also naturally occurring forms formed in the presence of the sun's UVB rays, hence the nickname "sunshine vitamin," but D2 is formed in plants and fungi and D3 in animals, including humans. Vitamin D production in the skin is the main natural source of vitamin D. However, many people have inadequate vitamin D levels because they live in places where sunlight is limited in winter, or because they have limited exposure to the sun because they spend most of their time indoors. In addition, people with darker skin usually have lower blood levels of vitamin D because the pigment (melanin) acts like a shadow and reduces vitamin D production (and also reduces the harmful effects of sunlight on the skin, including skin cancer).

Why Vitamin D is important to our Body?

The role of vitamin D in disease prevention is a popular area of research, but clear answers about the benefits of taking amounts in excess of the RDA are inconclusive. Although observational studies see a strong association with lower rates of certain diseases in populations that live in sunnier climates or have higher serum vitamin D levels, clinical trials in which people are given vitamin D supplements to affect a particular disease are not yet conclusive. This may be due to different study designs, different absorption rates of vitamin D in different populations, and different doses given to participants. Learn more about research on vitamin D and specific health conditions and diseases:

A- Strength of the muscles and the bones

Several studies link low vitamin D blood levels to an increased risk of bone fractures in older adults. Some studies suggest that vitamin D supplementation at certain levels may prevent such fractures, while others do not.

1- A meta-analysis of 12 randomized controlled trials involving more than 42,000 people over 65 years of age, mostly women, examined vitamin D supplementation with or without calcium, and with calcium or a placebo. The researchers found that higher intakes of vitamin D supplements - about 500-800 IU per day - reduced hip and spine fractures by about 20%, while lower intakes (400 IU or less) provided no benefit in preventing fractures.

2- A systematic review examined the effect of vitamin D supplements taken with or without calcium on the prevention of hip fractures (primary outcome) and fractures of any type (secondary outcome) in older men and postmenopausal women aged 65+ years. The study included 53 clinical trials with 91 791 participants living independently or in a nursing home or hospital. No strong association was found between the use of vitamin D supplements alone and the prevention of fractures of any type. However, a small protective effect against all types of fractures was found when vitamin D was taken with calcium. Vitamin D supplements containing 800 IU or less were used in all studies.

3- The double-blind, placebo-controlled, randomized vitamin D and OmegA-3 TriaL (VITAL) trial of 25,871 women and men aged 55+ and 50+ years, respectively, found no protective effect of vitamin D supplements on bone fractures. [79] Participants were healthy at baseline-representative of the general population and not selected for low bone mass, osteoporosis, or vitamin D deficiency-and received either 2,000 IU of vitamin D or placebo daily for approximately five years. Vitamin D did not reduce the incidence of overall bone fractures or hip or spine fractures.

Vitamin D can help increase muscle strength by preserving muscle fibers, which in turn helps prevent falls, a common problem that causes significant disability and death in the elderly. A combined analysis of several studies found that taking 700 to 1,000 IU of vitamin D per day reduced the risk of falls by 19% while taking 200 to 600 IU per day offered no such protection. However, the VITAL study, which involved healthy middle-aged men and women, did not find that a daily intake of 2,000 IU of vitamin D reduced the risk of falls compared with a placebo pill.

Although daily intake of up to 800 IU of vitamin D may benefit bone health in some older adults, caution is advised with very high-dose supplements. In a clinical trial in which women over 70 years of age received 500,000 IU of vitamin D once a year for five years, the risk of falls was 15% higher and the risk of fracture was 26% higher than in women receiving a placebo. It has been speculated that oversaturation of the body with a very high dose given infrequently may have resulted in lower blood levels of the active form of vitamin D, which might not have been the case with smaller, more frequent doses.

B- Cancer

Nearly 30 years ago, researchers noted an interesting relationship between colon cancer deaths and geographic location: people who lived at higher latitudes, such as in the northern United States, had higher colon cancer death rates than people who lived closer to the equator. Many scientific hypotheses about vitamin D and disease come from studies comparing sun exposure and disease rates in different countries. These studies can be a good starting point for further research, but do not provide the most definitive information. At higher latitudes, the sun's UVB radiation is weaker, which in turn tends to lower the vitamin D blood levels of people in these regions. This led to the hypothesis that low vitamin D levels could increase colorectal cancer risk.

Animal and laboratory studies have shown that vitamin D can inhibit the development of tumors and slow the growth of existing tumors, including those in the breast, ovary, colon, prostate, and brain. In humans, epidemiological studies show that higher serum vitamin D levels are associated with significantly lower rates of colon, pancreatic, prostate, and other cancers, with the evidence strongest for colon cancer.

However, no consistent association has been found in clinical trials:

The Women's Health Initiative study, which followed about 36,000 women for an average of seven years, found no reduction in colon or breast cancer risk in women who took 400 IU of vitamin D and 1,000 mg of calcium daily compared with women who took a placebo. Limitations of the study were noted:

1. The relatively low dose of vitamin D that was administered to
2. Some individuals in the placebo group chose to take additional calcium and vitamin D supplements on their own, which minimized the differences between the placebo group and the supplement group.
3. About one-third of the women who were given vitamin D did not take their supplements.
4. Seven years may be too short a time to expect a reduction in cancer risk.

In a large clinical trial called vitamin D and OmegA-3 TriaL (VITAL), 25,871 men and women over 50 years of age who did not have cancer at baseline were given either a 2,000 IU vitamin D supplement or a placebo daily for an average of five years. The results showed no significantly different rates of breast, prostate, and colorectal cancer between the vitamin D and placebo groups. The authors pointed out that a longer follow-up period would be needed to better assess the potential effects of supplementation, as many cancers take at least 5-10 years to develop.

Although vitamin D does not appear to be a major factor in reducing cancer incidence, evidence, including from randomized trials, suggests that higher vitamin D status may improve survival in the face of cancer.  In the VITAL trial, a lower cancer mortality rate was observed among those taking vitamin D, and this benefit appeared to increase over time after vitamin D initiation. A meta-analysis of randomized vitamin D trials, which included the VITAL trial, found a 13% statistically significant lower risk of cancer mortality among those taking vitamin D compared with placebo. These results are consistent with observational data suggesting that vitamin D has a stronger effect on cancer progression than on incidence.

C- Heart Problems

The heart is essentially a large muscle, and it has vitamin D receptors just like skeletal muscle. Immune and inflammatory cells that play a role in cardiovascular diseases such as atherosclerosis are regulated by vitamin D. The vitamin also helps keep arteries flexible and relaxed, which in turn helps control high blood pressure.

Almost 50,000 healthy males were monitored for 10 years as part of the Health Professionals Follow-up Study. Those with the lowest vitamin D levels were twice as likely to have a heart attack as men with the highest levels. Meta-analyses of epidemiologic studies have found that people with the lowest serum vitamin D levels had a significantly increased risk of stroke and other heart disease compared with those with the highest levels.

However, taking vitamin D supplements was not found to reduce cardiovascular risk. A meta-analysis of 51 clinical trials failed to demonstrate that vitamin D supplementation reduces the risk of heart attack, stroke, or death from cardiovascular disease. The VITamin D and OmegA-3 TriaL (VITAL) study reached the same conclusion; it followed 25,871 men and women without cardiovascular disease who took either a 2,000 IU vitamin D supplement or a placebo daily for a median of five years. No association was found between taking the supplements and a lower risk of serious cardiovascular events (heart attack, stroke, or death from cardiovascular causes) compared with the placebo group.

Source of Food:

Few foods are naturally rich in vitamin D3. The best sources are the meat of fatty fish and fish liver oils. Cheese, cow liver, and egg yolks all contain smaller amounts. Certain mushrooms contain some vitamin D2; in addition, some commercially available mushrooms contain higher amounts of D2 because they have been intentionally exposed to high levels of ultraviolet light. Many foods and supplements such as dairy products and cereal products are fortified with vitamin D.

1. Cod liver oil
2. Salmon
3. Swordfish
4. Tuna fish
5. Orange juice fortified with vitamin D
6. Vitamin D-fortified dairy and plant milk
7. Sardines
8. Beef liver
9. Egg yolk
10. Fortified cereals

Supplements containing vitamin D3 against vitamin D2

When you buy vitamin D supplements, you may see two different forms: Vitamin D2 and Vitamin D3. Vitamin D2 is derived from plants and is found in fortified foods and some supplements. Vitamin D3 is naturally produced in the human body and is found in animal foods. It is controversial whether vitamin D3 ("cholecalciferol") is better than vitamin D2 ("ergocalciferol") at increasing blood levels of the vitamin. A meta-analysis of randomized controlled trials comparing the effects of vitamin D2 and vitamin D3 supplements on blood levels found that D3 supplements tend to increase blood concentrations of the vitamin more and maintain those levels longer than D2. Some experts cite vitamin D3 as the preferred form because it is naturally produced in the body and is found in most foods that naturally contain the vitamin.

Ultraviolet light

Vitamin D3 can be formed by a chemical reaction in human skin when a steroid called 7-dehydrocholesterol is broken down by the sun's UVB light, or what is known as tanning rays. The amount of vitamin absorbed can vary greatly. The following conditions reduce exposure to UVB light and therefore vitamin D absorption:

1- Using sunscreen; properly applied sunscreen can reduce vitamin D absorption by more than 90%.

2- Wear clothing that completely covers the skin.

3- Spending little time outdoors.

4- Darker skin color due to higher levels of the pigment melanin, which acts as a type of natural sunscreen.

5- Older age, when 7-dehydrocholesterol levels drop and skin changes, a population is likely to spend more time indoors.

6- Certain seasons and living at northern latitudes above the equator where UVB light is weaker. People in Boston (USA), Edmonton (Canada), and Bergen (Norway) in the Northern Hemisphere cannot get enough vitamin D from the sun for 4, 5, and 6 months of the year, respectively. In the southern hemisphere, residents of Buenos Aires (Argentina) and Cape Town (South Africa) are able to obtain far less vitamin D from the sun during the winter months (June through August) than during the spring and summer months. The body stores vitamin D from summer sun exposure, but it must last for many months. In late winter, many people in these higher latitudes are undersupplied.

In general, tanning beds shouldn't be utilised, as excessive sun exposure might result in skin cancer from UV rays.

Symptoms of Weakness and Toxic Effect

Vitamin D deficiency can result from a deficiency in the diet, inadequate intake, or increased metabolic demand. If people do not consume enough vitamin D and do not expose themselves sufficiently to ultraviolet sunlight over a long period of time (see section above), a deficiency can develop. People who cannot tolerate or do not eat milk, eggs, and fish, such as those with lactose intolerance or who eat a vegan diet, are at higher risk for deficiency. Other people at high risk for vitamin D deficiency include:

1- People with inflammatory bowel disease (ulcerative colitis, Crohn's disease) or other conditions that interfere with normal fat digestion. Vitamin D is a fat-soluble vitamin that depends on the gut's ability to absorb fat from food.

2- People who are overweight usually have lower levels of vitamin D in their blood. Vitamin D accumulates in excess fat tissue but is not readily available to the body when it needs it. To achieve the desired level of vitamin D in the blood, a higher dose of vitamin D supplementation may be required. Conversely, blood levels of vitamin D increase when obese people lose weight.

3- People who have undergone gastric bypass surgery, which usually removes the upper part of the small intestine where vitamin D is absorbed.

Diseases resulting from prolonged vitamin D deficiency:

Rickets: a condition with soft bones and skeletal deformities in infants and children caused by failure of bone tissue to harden.

Osteomalacia: A condition in adults caused by weak and soft bones that can be reversed by nutritional supplementation. This differs from osteoporosis, in which the bones are porous and brittle and the condition is irreversible.

Toxic Effect

Vitamin D toxicity most often results from the ingestion of dietary supplements. The small amounts of the vitamin in food are unlikely to reach toxic levels, and strong sun exposure does not cause toxicity because the excess heat on the skin prevents the formation of D3. It is recommended that daily vitamin D supplements in excess of 4,000 IU not be taken unless under medical supervision.

1. Anorexia
2. Weight loss
3. Irregular heartbeat
4. Increased calcium levels in the blood cause blood vessels and tissues to harden, which could harm the heart and kidneys.

Important Information:

Unfortunately, the sun's rays in a sunny office or on a car ride don't help you get vitamin D because window glass completely blocks UVB ultraviolet light.