Vitamin D – risks and benefits

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Vitamin D is found in many food sources such as fish, eggs, fortified milk and cod liver oil. Sun contributes significantly to the production of vitamin D daily – 10 minutes of sun exposure a day is considered sufficient time to prevent a deficiency of vitamin D. Vitamin D term refers to different forms of this vitamin.

Two forms of vitamin D are important for humans: vitamin D2 and vitamin D3.

Vitamin D2 is synthesized by plants. Vitamin D3 is synthesized by humans when skin is exposed to the sun’s ultraviolet B (UVB). Some commercial food can be fortified with vitamin D2 or D3.


1. Overview
2. Why do we need vitamin D?
3. Sources of vitamin D
4. Risks

Why do we need vitamin D?

The roles of vitamin D include:

- Is essential for calcium and phosphorus metabolism and absorbed, which have various functions, especially in maintaining bone health.
- Is a regulator of immune system
- Can support the immune system fight some diseases (such as colds, for example)
- Reduce the risk of multiple sclerosis developing
- Can play a key role in boosting brain function even in old age
- Helps maintain normal body weight
- Reduce the severity and frequency of asthma symptoms and likelihood of hospitalization due to asthma
- Shown to reduce the risk of rheumatoid arthritis in women
- One of the forms of vitamin D could play a role in damage protection for low levels of radiation
- People who have adequate levels of vitamin D have a significantly lower risk of developing cancer compared with people who have lower values of it. Vitamin D deficiency is commonly found in cancer patients, no matter what their nutritional status is.

Sources of vitamin D

- Food – Very few foods in nature contain vitamin D. The flesh of fatty fish (such as catfish, tuna, mackerel) and fish liver oils are among the best sources.

Small amounts of vitamin D are found in beef liver, cheese and egg yolk. Vitamin D in these foods is as D3 and its metabolite 25 (OH) D3. Some mushrooms provide varying amounts of vitamin D2. Mushrooms that were exposed to ultraviolet light have high levels of vitamin D2.

- Exposure to sunlight – Most people need to absorb the necessary amount of vitamin D through exposure to ultraviolet rays of the sun: radiation with a wavelength of 290-320 nanometers penetrates uncovered skin and converts 7-dehydrocholesterol cutaneous in pre-vitamin D3 which converts to vitamin D3. Season, time of day, duration of exposure, cloud cover, smog, content of melanin in skin and sun protection are among the factors that affect exposure to ultraviolet radiation, and the synthesis of vitamin D.

Even if it seems surprising, geographic latitude not decisively predict average levels of serum 25 (OH) D in the population. There are ample opportunities for training of the vitamin D (and storage in liver and fat) by the sun during spring, summer and autumn, even in the northernmost latitudes. A completely cloudy sky reduces by 50% the ultraviolet energy from sunlight (including that produced by severe pollution). UVB rays do not penetrate through glass, so exposal to the sun through a window does not cause the production of vitamin D.

Sunscreens with a sun protection factor (SPF) of 8 or larger block vitamin D production by UVB rays. It is believed that skin synthesizes some forms of vitamin D even when people apply sunscreen on skin products.

Factors affecting exposure to UV radiation and research to clarify the time of sun exposure needed to maintain adequate levels of vitamin D make it difficult to provide general guidelines. Some researchers suggest that approximately 5-30 minutes of sun exposure without sunscreen to face, arms, legs and back, between 10-15, at least twice a week is enough to synthesize a sufficient amount of vitamin D. Using of sunbeds for tanning in moderation, that emit 2-6% UVB, is also effective. People with limited sun exposure should include good sources of vitamin D in their diet and use supplements to achieve recommended levels of it.

- Nutritional supplements – in the form of supplements or fortified foods, vitamin D is available in two forms: vitamin D2 or ergocalciferol and cholecalciferol vitamin D3, which differ chemically only in their structural part of the chain. Vitamin D2 is produced by radiating UV ergosterol in yeast, and vitamin D3 is produced by irradiating 7-dehydrocholesterol from lanolin and the chemical conversion of cholesterol. The two forms have been treated fairly because of their ability to cure rickets, stimulate metabolism.


Health risks of excessive consumption of vitamin D

Vitamin D toxicity can cause nonspecific symptoms such as anorexia, weight loss, polyuria and mild heart disorders. Worse, this can raise blood calcium levels, which can lead to tissue and vascular calcification, with subsequent damage to the heart, blood vessels and kidneys.

Use of calcium supplements (100mg/day) and vitamin D (400 IU) by postmenopausal women was associated with an increase of 17% of the risk of kidney stones, over seven years. Excessive sun exposure does not cause vitamin D toxicity, sustained heat as skin photo-degrades pre-vitamin D3 and vitamin D3 form. In addition, thermal activation of pre-vitamin D3 in the skin gives rise to various forms of non-vitamin D which limits the formation of vitamin D3 in itself. Some types of vitamin D3 are converted to inactive forms. Intake of vitamin D from foods that have high values of this vitamin, is unlikely to cause toxicity. Toxicity is more likely to occur from consumption of excessive intake of nutritional or food supplements that contain vitamin D.



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