[英语阅读]缺少日照影响抑郁症病人认知

Lack of sun may dim depressed people's thinking

众所周知，日照与情绪息息相关，最明显的例子就是季节性情感障碍——抑郁症的一种，其症状随着季节的变化而不同，通常是患者病情在秋冬季节加重，而光照多的季节得到缓解。但是，光照能影响人们思考和记忆，却是个新话题。根据一项最新的研究显示，经过两周的观察，生活在光照时间短条件下的抑郁症病人，其认知能力低于在光照时间较长气候生活，有同样病症的患者。

A jogger runs at the foothills of the Canadian rocky mountains near Calgary, Alberta November 20, 2007.

A lack of sunshine may cloud memory and other thinking or "cognitive" functions in some people with depression, a new study hints.

There is a well-known association between sunlight exposure and mood, the clearest example being seasonal affective disorder (SAD) -- a form of depression in which symptoms shift with the seasons, usually arising in the late fall and winter and improving in sunnier months.

But little is known about whether sunshine can affect thinking and memory.

For the new study, researchers at the University of Alabama at Birmingham looked at the correlation between NASA weather data and cognitive-test scores among more than 14,000 U.S. adults age 45 and older. All had taken part in a government study of stroke risk factors.

The researchers found that among people who had screened positive for depression, those who had been exposed to little sunshine over a two-week period tended to have lower cognitive scores than their counterparts who lived in sunnier climes.

Depressed adults from the least sunny areas were more than twice as likely to have impairments in memory and other cognitive functions as those with the greatest sun exposure.

The sunshine-cognition link was not seen in adults without depression, however.

The findings, published in the journal Environmental Health, do not prove that a lack of sun impairs depressed people's thinking -- or that basking in the sun will improve the situation.

"You obviously don't want to take any actions based on one study," lead researcher Shia T. Kent, a Ph.D. candidate at the Alabama university, told Reuters Health.

But in theory, he said, sunlight might affect cognition through the same pathways it is thought to impact mood. Sun exposure helps regulate levels of two hormones, melatonin and serotonin, that affect mood and are suspected of playing a role in SAD and general depression.

Recent research suggests that melatonin and serotonin are also involved in cognition.

"It may be that people who are more affected by sunlight exposure in terms of depression are also more affected in terms of cognition," Kent speculated.

The findings also raise the possibility that light therapy, which is a standard treatment for SAD, might improve depressed individuals' cognition as well.

Kent said that future studies of SAD patients, including those testing light therapy, should look at any potential effects on cognition.