Obesity is a risk factor for many chronic physical and mental illnesses. The health effects of being overweight but not obese are controversial, with some studies showing that the mortality rate for individuals who are classified as overweight (BMI 25.0 to 29.9) may actually be lower than for those with an ideal weight (BMI 18.5 to 24.9). Health risks for those who are overweight may be decreasing over time as a result of improvements in medical care. Some obesity-associated medical conditions may be the result of stress caused by medical discrimination against people who are obese, rather than direct effects of obesity, and some may be exacerbated by the relatively poor healthcare received by people who are obese.