Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2009
Publication Date: 4/1/2009
Citation: Ahmad, S.M., Haskell, M.J., Raqib, R., Stephensen, C.B. 2009. Vitamin A Stores Are Associated With T-Cell Responses In Bangladeshi Men. British Journal of Nutrition. 102:797-802.
Interpretive Summary: The recommended intake for vitamin A is based on maintaining normal vision. We have conducted a study to determine if the requirements for vision are also adequate to maintain normal immune function. We found that both the number of T lymphocytes in the blood, and their ability to proliferate when isolated, both increase when vitamin A stores increase above the level needed to maintain normal vision, although even subjects with the lowest level of vitamin A still had adequate immune function. This finding suggests that while low vitamin A stores maintain adequate immune function, increased stores may stimulate greater immune function which could be beneficial for resisting infectious disease but might be detrimental in people with some chronic inflammatory diseases where additional immune stimulation is not needed.
Technical Abstract: Recommendations for vitamin A intake are based on maintaining liver stores of equal to or greater than 0.070 umol/g, which is sufficient to maintain normal vision. We propose that higher levels may be required to maintain normal immune function. To test this hypothesis, we conducted an 8 wk residential study among 36 healthy Bangladeshi men with low vitamin A stores. Subjects were randomized to receive vitamin A (240 mg in 4 doses) or placebo during study wks 2 and 3. Vitamin A stores were estimated by isotopic dilution at wk 8. Total T-cells, the ratio of naïve-to-memory T-cells and mitogen-induced lymphocyte proliferation were positively and significantly correlated with vitamin A stores (P<0.05). Mitogen-stimulated IL-2, IL-4 and TNF' increased significantly (P<0.05) in the vitamin A but not placebo group after supplementation while IL-10 production was significantly and negatively correlated with vitamin A stores (P<0.05). Segmented linear regression analysis revealed that naïve T-cell counts and T-cell blastogenesis were positively associated with vitamin A stores and memory T-cell counts were negatively associated with stores above but not below 0.070 umol/g liver. These data show that increasing vitamin A stores above the level that maintains normal vision enhances some measures of T cell-mediated immunity, suggesting a difference in requirements for maintaining vision and immune function.