The effects of 13-cis-retinoic acid and beta-carotene on cellular immunity in humans

Article Abstract:

A large body of evidence has accumulated to suggest that a deficiency of vitamin A (retinol) or its precursors may be associated with an increased risk of cancer. Furthermore, some studies have indicated that related compounds, such as the retinoids and carotenoids, may exert an inhibiting influence on cancerous growth. One way in which these compounds may influence the development of cancer is through the modulation of the immune system, and studies have examined the influence of retinoids and carotenoids on the cellular immunity of both animals and humans. In the present study, 13-cis-retinoic acid, a retinoid, and beta-carotene, a carotenoid, were examined for their influence on immune function in 25 men with precancerous conditions. (Sixteen men had oral leukoplakia and nine had Barrett's esophagus.) The retinoic acid was found to increase the proportion of white blood cells with markers for the helper T cell. This compound had no effect, however, on the expression of markers for the natural killer cell, a cell thought to be important in the destruction of tumor cells. Beta-carotene, on the other hand, increased the percentage of apparent natural killer cells, but had a smaller effect on the proportion of helper cells. Since the doses used were well within the appropriate clinical range, the authors suggest that these compounds may prove useful in the modulation of the immune system. However, while a peak effect was seen about two months from the start of treatment, a slightly reduced effect was observed at three months. It is not yet certain whether chronic treatment with these compounds will sustain the observed changes in cellular immunity. (Consumer Summary produced by Reliance Medical Information, Inc.)

Vitamin A, Cellular immunity, Tretinoin, Retinoids, Carotenes

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Effect of beta-carotene on lymphocyte subpopulations in elderly humans: evidence for a dose-response relationship

Article Abstract:

Beta-carotene is an important nutrient; it is the form of vitamin A that is present in fruits and vegetables. In the body, beta-carotene can be transported in the blood, stored in tissues, or converted to retinol, the other form of vitamin A. Recent studies have suggested that beta-carotene may be beneficial in preventing cancer and in stimulating the immune system to fight infection. These effects of beta-carotene are believed to be independent of the conversion of beta-carotene to retinol. The effects of beta-carotene supplements on immune system function were evaluated in 20 healthy, older adults with an average age of 56 years (10 men and 10 women). Beta-carotene supplements, 30 milligrams/day for two months, resulted in a substantial increase in the percentage of cells with surface markers for natural killer cells and T-helper cells, as well as cells with interleukin-2 receptors (cells of the immune system required for killing invading organisms and stimulating antibody production). At the same time, the number of T-suppressor cells (cells that suppress the immune system) did not change. Plasma levels of beta-carotene were elevated, while plasma levels of retinol did not change. This indicates that the stimulatory effect of beta-carotene on the immune system does not involve conversion of beta-carotene to retinol. It is concluded that beta-carotene has properties that stimulate the immune system in humans, which may have potential in the prevention of cancer. (Consumer Summary produced by Reliance Medical Information, Inc.)

Immune system

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Premalignant lesions: role of antioxidant vitamins and beta-carotene in risk reduction and prevention of malignant transformation

Article Abstract:

Malignant transformation of a normal cell into a cancerous cell occurs in three phases: initiation, a genetic mutation occurring within the cell; promotion, a second stimulus required to activate the transformation; and progression, the development of a tumor. Premalignant lesions that have been associated with increased cancer incidence include Barrett's esophagus (chronic irritation of the esophagus by stomach acid), oral leukoplakia (white patches on the tongue and cheek), polyps in the colon, papillomas (tumor-like structures) in the bladder, and gastric (stomach) and cervical dysplasia (abnormal tissue development). Previous studies have shown a relationship between vitamin intake and cancer risk. Reduced dietary intake and blood levels of vitamin C and beta-carotene (the form of vitamin A found in fruits and vegetables) have been associated with an increased risk of cervical cancer, gastric cancer and lung cancer. Beta-carotene and vitamin C have proven beneficial in reducing the risk of developing oral leukoplakia (also known as smoker's tongue) and cervical dysplasia. Preliminary studies are encouraging, and further studies on the role of vitamins in reducing cancer risk should be performed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Vitamin C

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