Vitamin A is best known for prevention of night blindness and other eye problems. It aids to form the pigment in your eyes that is responsible for the functioning of the light sensitive part of the eye called the retina. Every time light comes into your eyes your body uses vitamin A compounds.

Helps keep the immune system healthy and low Vitamin A has been shown to lead to decreased immune function. This is of vital importance because it is the immune system that in turn helps prevent the body from being overrun by infections of the respiratory tract, such as the cold and flu virus, which are very common.

In both men and women it promotes a healthy reproductive system. In women, it is important for a healthy pregnancy and for producing milk.

It is critical for cell growth and development and needed for healthy skin and hair. Vitamin A has been used to prevent acne, boils and open skin sores.

It also acts an antioxidant which is extremely powerful against free radicals. Free radicals are produced as a consequence to us consuming oxygen. Oxygen, even though we can't live without it, causes oxidation something called free radicals. These disrupt cells and since they can quickly multiply, wreak havoc in our body. They are linked to the onset of death while antioxidants have been hailed as the fountain of youth, and rightly so. Antioxidants have been shown to help protect the body from cardiovascular disease and even cancer.

It was found that lycopene, which comes from tomatoes, has twice the antioxidant capability of Beta-carotene, which was once thought as the best. (1)

Vitamin A can be divided into two groups: retinoids and carotenoids.

Retinoids are preformed Vitamin A compounds. This means they are active so the body can use them immediately.

Carotenoids on the other hand, are precursors to Vitamin A meaning that the body can convert them to Vitamin A when needed. Some also acts as powerful antioxidants.
Caroteniods, which come only from plant sources, have a distinct advantage because even though they are fat-soluble, (meaning that they are stored with the aid of bodyfat) they do not appear to produce toxicity even at high levels. The body can regulate the amount of carotenoids that are converted to Vitamin A.

Pregnant women should take Vitamin A with the consideration of her doctor since large doses have been linked with miscarriages and birth defects. (2)
A Boston University study done on 23,000 pregnancies found that women who took more than 10,000IU per day early in their pregnancies actually had increased chances of birth defects. The researchers noted that beta-carotene seemed to be quite safe.

Large doses of beta-carotene have been linked with lung cancer in high risk cancer patients.
One study involving 18,000 former or current smokers or workers exposed to asbestos was conducted in 1986. They were taking 25,000 IU of Vitamin A plus 30mg of beta-carotene daily. The researchers ended the study early when they found 28% more lung cancers and 17% more deaths in the participants taking the supplements compared with a placebo. One must keep in mind, though, that these people were already at high risk for developing cancer.

Betacarotene:
6 mg (4)

(RODD)Recommended Optimal Daily Intake:
1000 g of preformed(retinol) VitA or about 5000 International Units (IU)
plus 6-15 milligrams of mixed carotenoids (5)

Be careful! Since Vitamin A is a fat soluble vitamin it can be stored in your body and excessive doses can cause toxicity. Choose Vitamin A sources such as Carotenoids which are similar biological activity to Vitamin A but have two advantages. They do not appear to cause toxicity when taken in high dosages since the body is better able to regulate the conversion to Vitamin A. They also have powerful antioxidant activity, giving you yet another reason to eat your fruits and vegetables.
If your nutrition intake is high in mixed carotenoids, most likely you don't need any extra supplementation of preformed Vitamin A.

Best sources are found in red, yellow and orange colored fruits and vegetables. They are found in carrots, sweet potatoes, pumpkins, spinach, broccoli, collard greens, peppers, turnip greens, and in fruits such as oranges, apricots, peaches, papayas and cantaloupes. It is these produces that have been shown to be responsible for the decrease in cancer, cardiovascular and eye disorders probably due to their antioxidant effects.

Adopted from Food and Nutrition, Australasia, Asia and the Pacific, Mark L. Wahlqvist, 1997

These are rough guidelines as there may be a lot of variance between where the food product came from and how it was processed. Both retinol and carotene are sensitive and get damaged by light and oxygen.

Immune System:

This is our body's defense system to foreign invaders and Vitamin A is essential for its effective performance.

  Zhao and Ross discovered in their research that retinoic (Vitamin A) activity was important in maintaining healthy levels of natural killer cells which have anti viral and anti-tumor activity.

  In 1992, Dr. Blomhoff confirmed that retinol activity was required for the growth, differentiation and activation of B lymphocytes, which are powerful immune system cells.

Cancer:

Carotenoids help prevent the formation of carcinogens which lead to tumor growth. They help separate and neutralize the bad chemicals and cells can return to normal growth. They also aid in reducing oxidative damage with their potent antioxidant effect.

  A nineteen year study of 1,954 middle-aged employees of the Western Electric Company in Chicago showed the effectiveness of carotenes in preventing lung cancer. Those that consumed the least amount of carotenes were seven times more likely to develop lung cancer compared to those that consumed the most. It's worth noting that those who took preformed Vitamin A did not experience these benefits. Yet another reason to increase your carotenoid intake (fruits and vegetables).

  One study in Switzerland tracked almost 3000 men over a period of twelve years and found out that those with low blood level of carotenoids had a higher death rate of cancer. In terms of stomach cancer, it was discovered that the survivors had 60% higher blood carotenoid levels compared to those that died.

  A study at the University of Washington, the diets of about 200 women with cervical cancer were compared to an almost equal number of women who were cancer free. The researchers in 1989 released their findings that high intakes of beta carotene were associated with a reduction in cervical cancer risk. Preformed Vitamin A showed no effect, in other words stick to carotenoids which come form plants.

  A British study collected 5004 blood samples from women were taken and frozen. Their health was monitored for several years in which time 39 patients developed breast cancer. When evaluating the blood samples it was discovered that the women with cancer had nearly 50% lower levels of beta-carotene compared to the healthy women.

  A study conducted at the University of Arizona looked at the effects of high doses(30milligrams) of beta-carotene daily for three months in patients with pre-cancerous lesions of the mouth called leukoplasia. They discovered that these lesions regressed partially or completely in 71% of the patients.

Eye Disorders:

  A study at Tufts University looked at blood levels of carotenes in about 100 men; some with cataracts and some without. They reported discovering that those in the lowest 20 per cent for beta-carotene in the blood were 5 times more likely to develop cataracts compared to those in the top 20 per cent.

  An aging related condition called macular degeneration is responsible for the breakdown of the part of the retina responsible for producing detailed images. This can lead to severe visual problems. Researchers suspected that oxidative damage causes or at least contributes to this breakdown. This is of course combated by antioxidants especially the carotenoids. To prove this, researchers looked at more than 1000 people to examine the antioxidant effect of beta-carotene on this condition. The results showed that those with the highest blood levels of carotenoids were one third less likely to develop macular degeneration compared with those with the lowest levels.

Cardiovascular Disease:

This is our country's number one killer of people over 40. Atherosclerosis which is the hardening and narrowing of the arteries, is brought about by the production of free radicals. They attack LDL cholesterol and help them discharge their fatty contents which can shut down most or all of the blood vessel. This leads to oxygen deprivation of the heart and heart failures. Fruit and vegetable based carotenoids due to their antioxidant effect prevent this from occurring. Thus the risk of atherosclerosis and heart attacks are substantially reduced.

  For about 11 years Harvard University monitored the health of almost 90,000 women. In 1991 they reported that those with high betacarotine intake decreased their risk of heart attacks. Those with the highest levels of beta carotene have 22% fewer heart attacks compared with the lowest levels.

  In another Harvard study, out of 333 men that were diagnosed of heart disease, those who supplemented with 50 milligrams of beta-carotene every other day had 44% lower risk of a major cardiovascular event. This was compared to a placebo (no active ingredients pill).

  A study published in 1992, monitored nearly 1300 men and women in the Boston area for 5 years. They discovered that those that consumed the greatest amounts of beta carotene had a 75% lower risk of death from a heart attack compared to those with the lowest consumption.

  The Journal of the American Medical Association reported a study in 1994 which looked at 3800 men with high cholesterol. The researchers found that those with the highest levels of carotenoids were 36% less likely to develop coronary heart disease tan men with the lowest levels.

  The National Institute of Public Health in the Netherlands studied 552 men for about 15 years. They concluded that those with the highest intakes of beta-carotene were 46% less likely to suffer a stroke compared to those with the least consumption.

HIV Infection:
Vitamin A and beta-carotene helps the immune system and this could be of particular importance to those individuals whose immune system is impaired, such as AIDS patients.

  John Hopkins University researchers compared Vitamin A levels of a group of 126 people that were tested positive for the HIV virus, to another group(53) who tested negative but were considered high risk for HIV infection. It was published in 1993 that those testing negative had about 25% higher levels of Vitamin A in the blood compared to those that tested positive. Deaths in the HIV group in the following years, were six times greater in those with inadequate Vitamin A levels. According to researchers Vitamin A, "seems to be an important risk factor in disease progression" in HIV patients.