London: You've heard of seasonal affective disorder, or Sad, when dark, cold winter days trigger the blues. But last week the UK's daily reported on another depression trigger: too much sun.

The journal cited up to 600,000 Britons suffering from "summer Sad," which is linked to sensitivity to heat and hormonal imbalances that can lead to lethargy and depression. An estimated 1.5 million Americans may suffer from summertime sad as well.

On July 1 website also reported on the phenomenon, noting that those affected with summer SAD sleep less, eat less, and lose weight, and may be extremely irritable during the long days of summer. For wintertime SAD, the reverse happens: More sleep, weight gain, and intense high-carb cravings often accompany a low mood.

"Summer-onset depression is thought to affect less than 1 percent of the population, making it much rarer than the winter variety experienced by an estimated 5 percent of people," states website.

WebMD cites that about 10 percent of people with SAD in the wintertime also get it in reverse in the summertime. The website also notes that some studies have found that in countries near the equator, such as India, summer SAD is more common than winter SAD.

Summer SAD is nothing new. It was first recognized in 1986 when mental health professionals suspected that heat and humidity contributed to depression.

Other summer depression triggers? WebMD cites disrupted schedules, body image issues, and financial worries due to expenses of summer holidays, babysitters, and camps for kids for working parents.

Ideas for relieving symptoms: Experts recommend staying cool with cold showers, air conditioning, swimming in cold lakes, or heading north to cooler climes if you can. Since people tend to drink more alcohol in the summer, according to daily, is mindful of your consumption, since alcohol is a depressant.

The long summer days may also be misaligning your circadian rhythms, experts say, so another treatment plan could involve a "combination of getting early morning sunlight (30 to 60 minutes daily), which shifts the body clock forward, and low-dose melatonin, a hormone that helps regulate sleep-wake cycles," notes website.

However if your symptoms are severe, you may benefit from antidepressants. Talk to your physician if you're struggling with a low mood this summer.