Vitamin A, as retinol, helps produce the pigment of the retina and, as retinoic acid, functions as a growth promoter in certain cells, notably the cells that form linings, such as in the respiratory and digestive tracts. Vitamin A also acts as an antioxidant, and considerable research has produced evidence for the important role vitamin A plays in the prevention and treatment of a number of health conditions.
Heart
Vitamin A contributes to heart health, according to researchers of a study published in the 2010 "Cell Physiology and Biochemistry" journal. In the study, vitamin A-deficient laboratory rats showed impaired heart structure and function. The rats' left ventricles -- the heart chamber that pumps blood out to the body -- were enlarged, and systolic blood pressure -- the lower number of the blood pressure ratio -- was weak, indicating a greater workload and less ability of the heart to pump blood. The vitamin A-deficient rats also showed increased oxidized lipids and the pro-inflammatory molecule tumor necrosis factor-alpha.
Respiratory and Digestive Systems
Vitamin A might protect against respiratory and intestinal diseases in children, say authors of a study published in the August 2010 "Science" journal. In the study, vitamin A-deficient rats showed increased production of inflammatory interleukin molecules and decreased secretion of the immunity molecules interferon and immunoglobulin-A. The vitamin A-deficient rats were more susceptible to infection with salmonella and also more susceptible to damage to the lining of the intestinal tract, according to the researchers.
Bone Health
Contrary to previous reports of detrimental effects of vitamin A on bone health, a study published in the January 2009 "American Journal of Clinical Nutrition" found no increased risk of fracture with high levels of vitamin A consumption. The study used data from more than 75,000 female participants of the Women's Health Initiative Observational Study and saw no increased incidence of hip fracture or total fractures. A slight increase in fracture risk occurred in women who had low vitamin D intake combined with high vitamin A intake.
Vision
Supplementation with a combination of the carotenoid lutein, a member of the vitamin A family, together with vitamin A, slows loss of vision in retinitis pigmentosa, an eye disease involving damage to the retina, according to a long-term study published in the April 2010 "Ophthalmology" journal. In the study, patients ages 18 to 60 took 12 mg of lutein and 15,000 international units, or IU, of vitamin A per day for four years. Loss of peripheral vision was slowest among those with the highest blood levels of lutein. There were no significant adverse side effects, and the researchers concluded that supplementation with lutein and vitamin A was effective at slowing the progression of visual loss in retinitis pigmentosa patients.
References
- "Cell Physiology and Biochemistry"; "Ventricular remodeling induced by tissue vitamin A deficiency in rats"; P.S. Azevedo et al; 2010
- "Nutrition"; "Effects of vitamin A deficiency on mucousal immunity and response to intestinal infection in rats"; Y. Yang et al; 2011
- "American Journal of Clinical Nutrition"; "Vitamin A and retinol intakes and the risk of fractures among participants of the Women's Health Initiative Observational Study"; G. Caire-Juvera et al; 2009
- "Archives of Ophthalmology"; "Clinical trial of lutein in patients with retinitis pigmentosa receiving vitamin A"; E.L. Berson et al; 2010
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