Unhappy people are relatively forgetful, a survey has found. The Hong Kong Memory Study Association found 90 per cent of people who said they were unhappy also felt their memory was worsening. Other reasons blamed for poor memory included working overtime, sleeplessness, tiredness and less than seven hours of sleep a day. And in one of the study's more unusual findings, people who dined out at least twice a day also said their memories were getting worse. The April study questioned 2,289 people aged six to 73, both female and male. Respondents were asked whether they felt their memories were better, worse or the same. They were also asked about their lifestyles, working hours, sleep, happiness in the past half year, dining habits and health. Association director Roy Lam Kin-tung said 40 per cent of people felt their memories were getting worse, while just 4 per cent said their memories were improving. He said that the ability of a person to remember things was not necessarily linked to age. 'Of the 126 respondents who said they are always unhappy, 114 felt their memories got worse,' he said, adding 70 per cent of those who said they were happy also said their memories have improved. Respondents were not asked why they were unhappy. Mr Lam said lack of sleep and tiredness were also found to affect memory, and these were linked to working overtime. 'We found that people, on average, who worked overtime every day, felt their memories were getting worse. These people often worked more than eight hours a day, with some working more than 17 hours a day,' he said. Neurologist Chin Kim-fai said clinical experience showed that depression and unhappiness could affect memory.