Positive Health Online

Abstract

PALACE and colleagues, Institute of Cardiovascular Sciences, St Boniface General Hospital Research Center, Winnipeg, Manitoba, Canada write that despite being one of the first vitamins to be discovered, the full range of biological activities for vitamin A still remains to be defined . The authors review (158 references) the properties of vitamin A and carotenoids and assembles information regarding the basic structure and metabolism of vitamin A and carotenoids as related to their antioxidant activities .

Background

Methodology

Results

and Conclusions: Carotenoids are a group of nearly 600 compounds, structurally similar to vitamin A. About 50 of carotenoids have provitamin A activity. Recent research has demonstrated that vitamin A, carotenoids and provitamin A carotenoids may be effective antioxidants for the inhibition of heart disease. Vitamin A needs to be obtained from the diet, the richest sources being green and yellow vegetables, dairy products, fruits and organ meats . Vitamin A is found as retinol, retinal and reinoic acid within the body. Because all these forms are toxic at high concentrations, they are bound to proteins in the extracellular fluids and inside cells. Vitamin A is stored mainly as long chain fatty esters and as provitamin carotenoids in liver, kidney and fat tissue. The antioxidant activity of vitamin A and carotenoids is conferred by the hydrophobic chain of polyene units which can quench singlet oxygen, neutralise thiol radicals and combine with and stabilise peroxyl radicals. The longer the polyene chain, the greater the peroxyl radical stabilising ability. Due to their structures, vitamin A and carotenoids can auto-oxidise when O2 tension increases and are thus most effective antioxidants at low oxygen tensions, typical of the physiological levels of oxygen found in body tissues. Epidemiological evidence suggests that vitamin A and carotenoids are important dietary factors for reducing incidence of heart disease . Despite the considerable discrepancy between results from human studies regarding this relationship, carefully controlled experimental studies continue to demonstrate that these compounds are effective in mitigating and defending against many forms of heart disease. More research is required, particularly regarding the relevance of how tissue concentrations rather than plasma levels relate to progression of tissue damage in heart disease. The authors review epidemiological, intervention trials and experimental evidence regarding the effectiveness of vitamin A and carotenoids for reducing heart disease.

Conclusion

References

Palace VP et al. Antioxidant potentials of vitamin A and carotenoids and their relevance to heart disease. Free Radical Biology and Medicine 26(5-6): 746-61. Mar 1999.