SATURDAY, Oct. 9 (HealthDayNews) -- Warm, sunny weather has a positive impact on mood, thinking and mental health, University of Michigan researchers say.

They found these benefits are most pronounced when a person travels south in the winter or spends time outside on a warm spring day. The effects are much less noticeable in other seasons. In fact, hot weather in the summer actually lowers mood.

"Being outside in pleasant weather really offers a way to re-set your mindset," study leader Matthew Keller said in a prepared statement.

"Everyone thinks weather affects mood, but the biggest tests of this theory in 2000 found no relationship, so we went back and found there are two important variables: how much time you spend outside and what the season is. If you go from winter to spring and spend enough time outside, there's a noticeable change," Keller said.

He and his colleagues analyzed the results of three studies that included more than 600 people from across the United States. They found the average optimal temperature for Americans is 72 degrees F, about room temperature. Mood decreases when the temperature is much higher or lower.

There were regional differences. Mood peaked at 65 degrees in Michigan and at 86 degrees in Texas.

For weather to improve mood, people had to spend at least 30 minutes outside in warm, sunny weather.

The study will appear in an upcoming issue of Psychological Science.

More information

The American Academy of Family Physicians has information about emotional health.