(NaturalNews) Being inactive increases the risk of developing depression or dementia, according to studies presented at a conference of the British Nutrition Foundation.According to Nannette Mutrie of the University of Strathclyde, researchers are coming to understand how important physical activity is for psychological health. She said that recent research suggests that exercise can be successfully used to treat depression. Conversely, people who do live inactive lifestyles are twice as likely to become depressed."It's only recently that people have begun to see the link between physical activity and mental health," Mutrie said. "It's important for increasing people's self esteem, general mood, coping with stress and even sleeping better. And we now have very strong evidence that physical activity can prevent depression."Also presented were the results of a study conducted by researchers from the University of Bristol. Researchers analyzed 17 prior studies that had examined the connection between physical activity and the incidence of Alzheimer's disease or other forms of dementia. The researchers concluded that people who were physically active had a 30 to 40 percent lower risk of developing dementia than people who were inactive. This effect was seen in both women and men.Professor Judy Buttriss, director general of the British Nutrition Foundation, said that the studies reinforced the importance of exercise as well as diet in remaining healthy over the long term."There has already, justifiably, been a lot of emphasis on good nutrition," Buttriss said, "but we must also find ways of helping people to be more physically active to ensure that they maintain health and quality of life in later years."The U.K.'s Department of Health recommends that adults spend at least 30 minutes engaging in moderate exercise five days per week, and that children have one hour of moderate exercise each day. However, more than 50 percent of adults, along with 40 percent of girls and 30 percent of boys, fail to reach these benchmarks.