Tag: vitamin a

Vitamin A

Overview

Vitamin A has essential actions in areas of health including:

  • helping cells reproduce normally — a process called “cellular differentiation.”
  • good vision — the first sign of a vitamin A deficiency is often poor sight at night.
  •  proper development of an embryo and foetus.
  • keeping skin and mucous membranes that line the nose, sinuses, and mouth healthy
  • playing a role in immune system function, growth, bone formation, reproduction, and wound healing.

Beta-carotene is synthesised in humans to form vitamin A and vitamin A activity from high intakes of carotenes seems not to produce adverse levels of vitamin A. The safety of beta-carotene itself will be discussed separately from vitamin A.

Vitamin A is fat-soluble and readily accumulates in the liver. Therefore, if taken at high dosages on a daily basis, the vitamin can easily accumulate to dangerous levels in the liver and other tissues. However, in nutritionally deprived populations who do not have a steady, sufficient intake of vitamin A, the same high dosages may be necessary as occasional supplements in order to prevent the severe health consequences of vitamin A deficiency. This makes the safety of vitamin A highly dependent on both the daily level of intake and the duration of consumption.

Uses

Acne, Psoriasis, Eczema and other Skin disorders
Vitamin A can help clear up severe acne and psoriasis and have shown promise for treating other skin disorders, premature aging from the sun and warts.

Eye Disorders
Getting enough vitamin A in your diet is essential for good vision. Research shows that people who eat more foods with vitamin A are less likely to develop age-related macular degeneration. In addition, a large population study found that people who got high levels of vitamin A though their diets had a lower risk of developing cataracts. Vitamin A supplements may help slightly slow down the damage from retinitis pigmentosa, a hereditary disease that causes poor night vision.

Measles
For children who have vitamin A deficiency, supplements can reduce the severity and complications of measles. Children who are deficient in vitamin A are more likely to develop infections, including measles. In areas of the world where vitamin A deficiency is widespread or where at least 1% of those with measles die, the World Health Organization recommends giving vitamin A supplements to children who have measles. However, vitamin A does not seem to help unless a child has vitamin A deficiency. Never give a child high-dose vitamin A supplements without expert supervision.

Inflammatory Bowel Disease (IBD)
People with IBD, both ulcerative colitis and Crohn’s disease, may have a hard time absorbing all the nutrients their bodies need. Health care providers often recommend that people with IBD take a multivitamin, including vitamin A.

Cancer
Whether vitamin A can reduce the risk of cancer is not clear. People who eat a healthy diet with enough beta-carotene and other carotenoids from fruits and vegetables seem to have a lower risk of certain cancers, such as breast, colon, oesophageal, and cervical cancer. And some laboratory studies suggest that vitamin A and carotenoids may help fight certain types of cancer in test tubes.

One preliminary study suggests that a topical form of vitamin A may reduce abnormal growth of cells on the cervix, called cervical neoplasia.

Researchers are also investigating retinoids, a synthetic form of vitamin A, for skin cancer. People with certain types of skin cancer tend to have lower levels of vitamin A and beta-carotene in the blood.

Sources

Vitamin A, in the form of retinyl palmitate, is found in beef, calf, and chicken liver; eggs; fish liver oils; and dairy products, including whole milk, whole milk yoghurt, whole milk cottage cheese, butter, and cheese.

The body can also make vitamin A from beta-carotene and other carotenoids, fat-soluble nutrients found in fruits and vegetables that give them their colour. Most dark-green leafy vegetables and deep yellow/orange vegetables and fruits — sweet potatoes, carrots, pumpkin and other winter squashes, cantaloupe, apricots, peaches, and mangoes — contain substantial amounts of beta-carotene. By eating these beta-carotene rich foods, you can increase levels of vitamin A in your body.

Upper intake limits and risks

Regular intakes of excess vitamin A can lead to liver abnormalities (25,000 IU), bone fragility (27,000 IU) and birth defects (30,000 IU).

The Council for Responsible Nutrition considers supplements of 10,000 IU (3,000 µg) per day of preformed retinol to be safe for most people. As stated earlier, the recommendations for nutritionally replete populations must be considered separately from nutritionally deprived populations. In addition, even within nutritionally replete populations, intake from food sources can vary widely. Therefore, for people who consume high levels of vitamin-A-fortified foods or liver, a lower limit of 5,000 IU (1,500 µg) per day is recommended.

Beta Carotene

Overview

Beta-carotene is one of many hundreds of food carotenoids. Beta-carotene is the most abundant form of provitamin A (material that can be converted into vitamin A) in fruits and vegetables. It gives yellow and orange fruits their rich colours. Beta carotene is an effective source of vitamin A in both conventional foods and vitamin supplements, and is generally safe.

Beta-carotene is an antioxidant. It protects the body from damaging molecules called free radicals. Free radicals damage cells through a process known as oxidation. Over time, this damage can lead to a number of chronic illnesses. There is good evidence that eating more antioxidants foods helps boost your immune system, protect against free radicals, and may lower your risk of heart disease and cancer.

Studies have shown that people with high intakes of beta-carotene or high blood levels of this nutrient have a reduced risk of various diseases, including cancer and heart disease (van Poppel and Goldbohm 1995).  In addition, beta-carotene and some other carotenoids may play an important role in facilitating cell-to-cell communications (Acevedo and Bertran 1995). Because many carcinogens inhibit such cellular communications (Gregus and Klaasen 1996), protection of this activity by dietary substances could be an important function in the protection against cancer.

Dietary Sources

The richest sources of beta-carotene are yellow, orange, and green leafy fruits and vegetables (such as carrots, spinach, lettuce, tomatoes, sweet potatoes, broccoli, cantaloupe, and winter squash). In general, the more intense the colour of the fruit or vegetable, the more beta-carotene it has.

Beta-carotene is fat-soluble, so you should take it with meals containing at least 3 g of fat to ensure absorption.

Limits and safety levels

Extensive data show that beta-carotene supplements of 50 mg every other day (the equivalent to 25 mg per day) can be taken for more than a decade without harm in a large group of mostly nonsmokers (Hennekens et al. 1996). The Council for Responsible Nutrition concludes that an intake of 25 mg per day is acceptable for non-smokers. Skin discolouration may occur with larger amounts, but this effect is harmless and self-correcting with intake reduction.

The only evidence of adverse effects of beta-carotene comes from the ATBC and CARET studies, which involved long-term heavy smokers and asbestos workers. These data suggest a LOAEL of 20 mg per day for smokers or asbestos workers, but disparities between the ATBC and CARET results and other data prevent confident identification of any LOAEL for beta-carotene. Smokers and asbestos workers should first control these health risks, then evaluate whether beta-carotene supplements are necessary.

Sources

University of Maryland Medical Center