Some people will spend lots of money to keep themselves feeling younger for longer. But researchers believe there are actually plenty of cheap — and easy — ways to help keep our minds healthier as we get older. And a new study has found that eating fish may be linked to a lower risk of cognitive decline. An international team of researchers looked at 35 previous studies on the effects of eating fish on cognitive function. They found that those who ate the most fish had a lower likelihood of cognitive decline compared to those who ate the least. Cognitive decline — or impairment — refers to the difficulty that older adults have with thinking, learning, remembering, decision-making and concentrating. But it's not just normal aging: the term is used to describe a situation where a person's brain functions have changed more than is usually expected as we get older. It can happen suddenly or over time. And with more people living longer than ever before, experts think we will see more cases of cognitive decline, as well as more cases of conditions like dementia and Alzheimer's disease. The study found that the risk of cognitive impairment decreased the more fish people ate, starting from about 50 grams per day. However, the same pattern was not observed with dementia and Alzheimer's disease. The study authors said that more research would be required to look into the effects of fish on these conditions. In some parts of the world, fish are a very important part of the diet. But many people in countries like the UK and the US don't eat enough fish, experts say. Fish contain a range of vitamins and minerals, as well as omega-3 fatty acids, which have been linked to brain and heart health. However, some experts are worried that our polluted rivers, lakes and oceans are making fish less safe to eat.