Intake of folic acid (FA) in very high amounts leads to conditions similar to those of metabolic deficiency in folate⁽Reference Troen¹⁾. In a similar way, vitamin B₁₂ status influences the physiological response to different FA doses in the organism⁽Reference Morris²⁾. Several studies relate both the shortage of folate as well as its excess with a change in the immune response⁽Reference Field³⁾. Similarly, it has been found that vitamin B₁₂ may play an important role in cellular immunity. Therefore, an imbalance between the status of vitamin B₁₂ and FA could exacerbate the immune response⁽Reference Smith⁴⁾.

The aim of this study was to evaluate the global effect of different levels of dietary FA and vitamin B₁₂ on several parameters of the immune response in aged rats.

Twenty-month male Sprague–Dawley rats (n=40) divided into four groups were fed during 30 days with differently supplemented diets:

• CON_B12/CON_FA (50 μg vitamin B₁₂; 2 mg FA)

• DEF_B12/DEF_FA (0 μg vitamin B₁₂; 0 mg FA)

• DEF_B12/CON_FA (0 μg vitamin B₁₂; 2 mg FA)

• DEF_B12/SUP_FA (0 μg vitamin B₁₂; 8 mg FA)

We evaluated the natural killer (NK) cytotoxicity in spleen, thymus and axillary nodes and lymphocyte subsets in peripheral blood.

There was a significant decrease in the NK cytotoxicity in the spleen, in the DEF_B12/CON_FA group (P<0.05), but neither in the thymus nor the axillary nodes. Furthermore, we observed a significant decrease in the CD45 lymphocyte subsets in the groups DEF_B12/CON_FA and DEF_B12/SUP_FA (P<0.05) but not in lymphocyte subsets CD4, CD8, CD3 and CD161.

An imbalance between B₁₂ and FA concentrations during ageing alters some immunological parameters such as the NK citotoxicity and CD45 lymphocyte subsets. These effects have not been observed in a control (CON_B12/CON_FA) situation or even during deficiency of both vitamins (DEF_B12/DEF_FA). Therefore, the balance between the intake of folate and vitamin B₁₂ could be as important as their absolute concentrations in the diet.