Keeping your heart fit and strong can slow down the ageing of your brain, US researchers say. A Boston University team found healthy people with sluggish hearts that pumped out less blood had "older" brains on scans than others. Out of the 1,500 people studied, the team observed that the brain shrinks as it ages. A poor cardiac output aged the brain by nearly two years on average, Circulation journal says. The link was seen in younger people in their 30s who did not have heart disease, as well as elderly people who did. Lead researcher Dr Angela Jefferson said: "These participants are not sick people. A very small number have heart disease. The observation that nearly a third of the entire sample has low cardiac index and that lower cardiac index is related to smaller brain volume is concerning and requires further study." The participants with smaller brain volumes on magnetic resonance imaging did not show obvious clinical signs of reduced brain function. But the researchers say the shrinkage may be an early sign that something is wrong. More severe shrinkage or atrophy occurs with dementia. Dr Jefferson said there were several theories for why reduced cardiac index - how much blood the heart pumps out relative to body size - might affect brain health. For example, a lower volume of blood pumping from the heart might reduce flow to the brain, providing less oxygen and fewer nutrients needed for brain cells. "It is too early to dole out health advice based on this one finding but it does suggest that heart and brain health go hand in hand," she said. Experts say a person's cardiac index is fairly static - meaning it would be difficult to change it if it were low, without doing pretty intensive exercise training. Dr Clinton Wright, a brain and memory expert from the University of Miami, said: "Whether lower cardiac index leads to reduced brain volumes and accelerates neurodegeneration on an eventual path to dementia is not yet clear. "To address the health needs of our ageing population, a better understanding of the links between cardiovascular disease and brain structure and function will be required." The Boston School of Medicine team will now continue to study the individuals in the trial to see if and how the brain changes affect memory and cognitive abilities over time. Source: CNN