Effect of Fruit and Vegetable Consumption on Immune Function in Older People: a Randomized Controlled Trial

Background: Fruit and vegetable (FV) intake, which is often low in older people, is associated with reduced chronic disease risk.

Objective: We determined whether increased FV intake improves measures of immune function.

Design: We conducted a randomized controlled trial (The Ageing and Dietary Intervention Trial) in 83 healthy volunteers aged 65-85 y with low FV intakes (≤2 portions/d); 82 subjects completed the intervention. Participants were assigned to continue their normal diets or to consume ≥5 FV portions/d for 16 wk. At 12 wk, tetanus toxoid (0.5 mL intramuscular) and Pneumovax II vaccine (0.5 mL intramuscular; both vaccines from Sanofi Pasteur) were administered. FV intake was monitored by using diet histories, and biomarkers of nutritional status were assessed. The primary endpoint was the antibody response to vaccination. Specific antibodies binding to tetanus toxoid (total IgG) and pneumococcal capsular polysaccharide (total IgG and IgG2) were assessed at baseline and 16 wk. Participants were recruited between October 2006 and June 2008.

Results: The change in FV consumption differed significantly between groups [mean change in number of portions (95% CI): in the 2-portion/d group, 0.4 portions/d (0.2, 0.7 portions/d); in the 5-portion/d group, 4.6 portions/d (4.1, 5.0 portions/d); P < 0.001)] and also in micronutrient status. Antibody binding to pneumococcal capsular polysaccharide (total IgG) increased more in the 5-portion/d group than in the 2-portion/d group [geometric mean (95% CI) of the week 16:baseline ratio: 3.1 (2.1, 4.4) and 1.7 (1.3, 2.1), respectively; P = 0.005)]. There was no significant difference in the increases in antibody binding to tetanus toxoid.

Conclusion: Increased FV intake improves the Pneumovax II vaccination antibody response in older people, which links an achievable dietary goal with improved immune function.