Improved life expectancy is a triumph of modern medicine. However, today’s senior citizens are predicted to soon consume 75% of the available health-care resources. Identifying new strategies to promote a healthy ageing process has thus become a priority. In contribution to the research field of healthy ageing this thesis is focused on the health and gut function of older adults. Paper I explored ‘optimal functionality’; a new approach to put the older adult’s own perspectives on health in focus. According to the results a plethora of factors related to the body, the self and the external environment needs to be considered in order to create a comprehensive understanding of the health experience in old age. Paper II characterised senior orienteering athletes as a new model of healthy ageing, due to their significantly better percived health as compared to other free-living older adults; in particular they report better gut health. As the gut is important to health maintenance and immune function paper III explored inflammation and oxidative stress in senior orienteering athletes, and older adults with gut problems, generally finding low levels in both groups. Subsequently, Paper IV investigated the health status of free-living older adults in Örebro County and also reports the results from a randomised controlled trial evaluating the effect of a probiotic supplement on self-reported health and gut symptoms. Two-thirds of the included older adults reported gut problems, however, the probiotic intervention failed to show any effects. This thesis provides additional perspectives on older adults health and gut function, by concluding that 1) optimal functionality may be a useful concept to map areas of importance to the older adult’s health experience, 2) senior orienteers may be regarded as a suitable model to study healthy ageing, 3) the prevalence of gut problems among the general population of Swedish older adults is high, but was not improved by probiotic supplementation with Lactobacillus reuteri.