The Japanese researchers supplemented the diet of vitamin-C deficient mice with either the recommended 20 mg/kg of vitamin C per day or a high dose of 200 mg/kg per day for a year.
Published in the British Journal of Nutrition, the study sought to examine the influence of the vitamin on the number and function of immune cells, something the authors said was so far poorly understood.
After a year they measured the weight of immune organ the thymus and the number of immune cells in the peripheral blood, spleen and thymus. The results showed a high vitamin C intake could inhibit the age-related decrease in the size of the thymus and maintain thymic output, meaning stable immune cell counts as the mice aged. They said the finding could point to solutions for maintaining immune functions in elderly people.
The thymus, a small gland found at the base of the neck, grows until puberty in humans after which it degenerates as part of the ageing process. It is a key site for the development and differentiation of T-cells - types of white blood cells key to the immune system.
"Chronic involution of the thymus is thought to be one of the major factors contributing to the decline of immune function with increasing age," the researchers wrote.
T cells counts were significantly higher in the high dose vitamin C group when compared to the lower dose, according to researchers from the House Wellness Foods Corporation and the Tokyo Metropolitan Institute of Gerontology.
They said the change to the thymus may be due to vitamin C's promotion of the production of fibronectin, laminin and collagen.
The current recommended daily allowance for vitamin C is 75–90 mg per day in the US and 100 mg/d in Germany, Switzerland, Austria and Japan. The 'recommended' amount given to one of the groups was estimated according to this 100 mg/d figure and the average weight of the mice.
In the European Union there are two approved health claims related to vitamin C and the immune system. The first states: "Vitamin C contributes to the normal function of the immune system." While a second more specific claim states: "Vitamin C contributes to maintain the normal function of the immune system during and after intense physical exercise."
Source: British Journal of Nutrition
Volume 113, issue 4, pp. 603-609, doi:10.1017/S0007114514003857
"High dietary intake of vitamin C suppresses age-related thymic atrophy and contributes to the maintenance of immune cells in vitamin C-deficient senescence marker protein-30 knockout mice"
Authors: R. Uchio, Y. Hirose, S. Murosaki1, Y. Yamamoto1and A. Ishigami