According to a study by Harvard University, the risk of dementia has decreased by about 13% every decade in the past 27 years, mainly due to the decrease in the number of men. Among them, the average risk of dying from dementia in Britain fell by 22%, while that of women seemed to remain unchanged. Except for Britain, developed countries in Europe and the United States have shown similar trends. Currently, in western countries, women have the same risk of dementia as men. In 1995, 75 year old people in Europe and the United States had a one in four chance of suffering from dementia, but now it is less than one fifth. The study was published in the Journal of neuroscience. Researchers are also puzzled by this phenomenon, but many say the result may be related to people’s healthier lifestyle than before. Dr. Hoffman of Harvard University said there had been previous evidence of a decline in the prevalence of dementia, but he wanted to confirm this with the most reliable research so that researchers could find out why. According to Hoffman, there are two possible reasons: one is more effective cholesterol lowering drugs, and the other is the decrease of male smokers, both of which contribute to the improvement of heart health; the other is the improvement of population education level. Well educated people with strong cognitive ability may be more effective in preventing Alzheimer’s disease. According to the report, < / P > < p > dementia is considered to be one of the biggest health threats facing human beings in the 21st century. Globally, it is estimated that about 50 million people are ill, and by 2050, the number is expected to triple. However, researchers say that in high-income countries, dementia may not be as damaging to society as initially feared. If the decline continues, they say, there will be 15 million fewer cases in high-income countries than previously expected.