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Improving the immunity of older adults: Can eating fruit and vegetables help?1
Ageing is associated with a decline in immune function2 and increased risk of infection3 which may adversely affect nutritional status4. Older populations have low intakes of fruit and vegetables (F&V)5,6, and it is possible that increasing F&V consumption may benefit the health of older people. Indeed, several of the micronutrients associated with F&V-rich diets, such as carotenoids, flavonoids and vitamin C, have been shown to have a beneficial effect on immune function7. We therefore carried out a randomised controlled trial to examine whether increasing F&V intake could improve immune function in older adults.
The Ageing and Dietary Intervention Trial (ADIT)
We randomised 83 healthy volunteers aged 65-85 years with low F&V intakes (≤2 portions/day) to either increase their F&V intake to five portions/day, or to follow their normal diet (≤2 portions/day) for 16 weeks. A portion was based on the Food Standards Agency guidelines i.e. an 80g serving (e.g. one apple, orange or banana, three heaped tbsp of vegetables, or 150ml fruit juice). At week 12, participants were administered a Tetanus and Pneumovax II (both 0.5 mls intramuscular) vaccine. Antibody response was assessed as a clinically relevant marker of immune function (total IgG for tetanus and total IgG and IgG2 for pneumococcal capsular polysaccharide).
We designed the study in a way that reflected a ‘real life’ setting whereby participants consumed their preferred F&V. Participants were not offered a prescriptive list of F&V at any time during the study. Rather, consumption of a wide variety of F&V was encouraged and the five portions/day F&V dose was designed to be achievable and in line with the ‘5-a-day’ public health recommendations.
Compliance with the intervention
Compliance was closely monitored throughout the intervention by diet history and by assessing biomarkers of micronutrient status. One-to-one dietetic advice was provided to help participants’ incorporate the F&V into their daily diet. Participants also received a free, weekly home delivery of F&V.
At the start of the study, participants were consuming on average 1.4 portions of F&V/day. This changed significantly over the 16 weeks with those in the five portions/day group having a larger increase in F&V intake compared to those in the two portions/ day group (mean F&V increase 4.6 versus 0.4 portions, respectively). Greater changes in micronutrient status (vitamin C, zeaxanthin, β-cryptoxanthin and lycopene) were also evident in the five portions/day group compared to the two portions/day group.
Increasing F&V intake improved immune function
Those assigned to the five portions/day group had a greater antibody response to the Pneumovax II vaccine compared to those who continued to eat a low F&V diet. Antibody binding to the pneumococcal capsular polysaccharide (total IgG) increased significantly in the five portions/day group compared to the two portions/day group (geometric mean (95% CI) of week 16 to baseline ratio: 3.1 (2.1,4.4) and 1.7 (1.3,2.1), respectively; p=0.001). This was particularly evident in those who had never received the Pneumovax II vaccine before. An extra portion of F&V/day was estimated to increase total IgG and IgG2 response by 18% and 17%, respectively. We found no difference between the two groups in immune response to the tetanus vaccine.
Public health relevance
Although it’s not entirely clear what the link is between F&V and the enhanced immune response, our results suggest that increased F&V intake in some way boosted the function of the T-cell antibody pathway, resulting in greater immune response. Given that immune systems of older adults are less effective than that of younger individuals and are characterised by higher rates of chronic disease and susceptibility to infection, our findings have potential public health impact, particularly when considering the impact of vaccination programmes.
Encouraging endorsement of the ‘5-a-day’
With the continuing growth in our older population, it is important that more research is undertaken to examine how diet can help to support a healthy immune system. We have shown for the first time that consuming five portions of F&V/day improves antibody response to the Pneumovax II vaccine in older adults. Our findings thus provide a rationale for encouraging older adults to ‘eat 5-a-day’.
- Gibson A, et al. Effect of fruit and vegetable consumption on immune function in older people: a randomised controlled trial. Am J Clin Nutr 2012;96:1429-36.
- Dorshkind K, et al. The ageing immune system: is it ever too old to become young again? Nature Rev Immunol 2009;9:57-62.
- Garibella S. Vitamin and mineral supplements for preventing infections in older people. BMJ 2005;331:304-5.
- Meydani M. Nutrition interventions in aging and age-associated disease. Proc Nutr Soc 2002;61:165-71.
- Appleton KM, et al. Fruit and vegetable consumption in older people in Northern Ireland: levels and patterns. Br J Nutr 2009;102:949-53.
- Wakimoto P & Block G. Dietary intake, dietary patterns, and changes with age: an epidemiological perspective. J Gerontol A Biol Sci Med Sci 2001;56:S65-S80.
- Webb AL & Villamor E. Update:effects of antioxidant and non-antioxidant vitamin supplementation on immune function. Nutr Rev 2007;65:181-217.