Many countries are facing aging populations, with those over 65 years of age likely to represent the largest population over the next 10-20 years. Living longer often comes with poor health and, in particular, a decline in the immune function characterized by poor vaccine responses and increased risk of infection and certain cancers. Aging and diet represent major intrinsic and extrinsic factors that influence the makeup and activity of resident intestinal microbes, the microbiota, the efficient functioning of which is essential for sustaining overall health and the effectiveness of the immune system. The provision of elderly specific dietary recommendations appears to be lacking but is necessary since this population has an altered microbiota and immune response and may not respond in the same way as their healthy and younger counterparts. We have reviewed the evidence supporting the role of diet and, in particular, dietary carbohydrate, protein, and fat in influencing the microbiota and its generation of key metabolites that influence the efficient functioning of immune cells during aging, and how dietary intervention might be of benefit in improving the intestinal health and immune status in the elderly.

Ageing is characterized by immunosenescence and the progressive decline in immunity in association with an increased frequency of infections and chronic disease. This complex process affects both the innate and adaptive immune systems with a progressive decline in most immune cell populations and defects in activation resulting in loss of function. Although host genetics and environmental factors, such as stress, exercise and diet can impact on the onset or course of immunosenescence, the mechanisms involved are largely unknown. This review focusses on identifying the most significant aspects of immunosenescence and on the evidence that nutritional intervention might delay this process, and consequently improve the quality of life of the elderly. We would like to thank the reviewers for their careful review of our manuscript, which has been revised accordingly. Below, we have provided a point-by-point reply to the issues raised: AbstractAgeing is characterized by immunosenescence and the progressive decline in immunity in association with an increased frequency of infections and chronic disease. This complex process affects both the innate and adaptive immune systems with a progressive decline in most immune cell populations and defects in activation resulting in loss of function. Although host genetics and environmental factors, such as stress, exercise and diet can impact on the onset or course of immunosenescence, the mechanisms involved are largely unknown. This review focusses on identifying the most significant aspects of immunosenescence and on the evidence that nutritional intervention might delay this process, and consequently improve the quality of life of the elderly.

Amongst the major features of aging are chronic low grade inflammation and a decline in immune function. The Mediterranean diet (MedDiet) is considered to be a valuable tool to improve health status, and although beneficial effects have been reported, to date, immunological outcomes have not been extensively studied. We aimed to test the hypothesis that 1 year of a tailored intervention based on the MedDiet with vitamin D (10 μg/day) would improve innate immune responses in healthy elderly subjects (65–79 years) from the English cohort (272 subjects recruited) of the NU-AGE randomized, controlled study (clinicaltrials.gov, NCT01754012). Of the 272 subjects forming the United Kingdom cohort a subgroup of 122 subjects (61 in the intervention group and 61 in the control group) was used to evaluate ex vivo innate immune response, phenotype of circulating immune cells, and levels of pro- and anti-inflammatory markers. Odds Ratio (OR) was calculated for all the parameters analyzed. After adjustment by gender, MedDiet-females with a BMI < 31 kg/m2 had a significant upregulation of circulating CD40+CD86+ cells (OR 3.44, 95% CI 1.01–11.75, P = 0.0437). Furthermore, in all MedDiet subjects, regardless of gender, we observed a MedDiet-dependent changes, although not statistically significant of immune-critical parameters including T cell degranulation, cytokine production and co-receptor expression. Overall, our study showed that adherence to an individually tailored Mediterranean-like dietary pattern with a daily low dose of vitamin D3 supplements for 1 year modified a large variety of parameters of immune function in healthy, elderly subjects. We interpreted these data as showing that the MedDiet in later life could improve aspects of innate immunity and thus it could aid the design of strategies to counteract age-associated disturbances.Clinical Trial Registration: clinicaltrials.gov, NCT01754012.

IntroductionAging is accompanied by increased susceptibility to infection and age-associated chronic diseases. It is also associated with reduced vaccine responses, which is often attributed to immunosenescence and the functional decline of the immune system. Immunosenescence is characterized by a chronic, low-grade, inflammatory state termed inflammaging. Habitants of Mediterranean (MED) regions maintain good health into old age; often attributed to MED diets.HypothesisAdoption of a MED-diet by elderly subjects, in Norfolk (UK), may improve immune responses of these individuals and in particular, dendritic cell (DC) function.Experimental approachA total of 120 elderly subjects (65–79 years old) recruited onto the Nu-AGE study, a multicenter European dietary study specifically addressing the needs of the elderly, across five countries, and were randomized to the control or MED-diet groups, for one year. Blood samples were taken pre- and post-intervention for DC analysis and were compared with each other, and to samples obtained from 45 young (18–40 years old) subjects. MED-diet compliance was assessed using high performance liquid chromatography-with tandem mass spectrometry analysis of urine samples. Immune cell and DC subset numbers and concentrations of secreted proteins were determined by flow cytometric analysis.ResultsAs expected, reduced myeloid DC numbers were observed in blood samples from elderly subjects compared with young. The elevated secretion of the adipokine, resistin, after ex vivo stimulation of peripheral blood mononuclear cells from elderly subjects, was significantly reduced after MED-diet intervention.ConclusionThis study provides further evidence of numerical and functional effects of aging on DCs. The MED-diet showed potential to impact on the aging immune cells investigated and could provide an economical approach to address problems associated with our aging population.