Daylight saving time ends this weekend in Europe and next weekend in the U.S., but extending it could help couch potatoes get more exercise and might also reduce the incidence of depression, a British social policy scholar argues.

"It must be rare to find a means of vastly improving the health and well-being of nearly everyone in the population; here we have it," Mayer Hillman, PhD, of the University of Westminster in London, wrote online in BMJ.

For more than 20 years, Hillman has been crusading for year-round daylight saving time -- plus an extra one-hour shift in summer. He cites a range of projected benefits: reduced energy use, fewer darkness-related car crashes, greater economic productivity -- and, oh yes, improved health, the focus of his BMJ essay.

Hillman -- trained in architecture and urban planning -- is well known in Britain for his advocacy of new models of transportation and development that emphasize walking and bicycling. He has also made controversial calls for drastic action to forestall climate change.

In the BMJ article, he contended that pushing sunrise and sunset forward an hour in winter and two hours in summer would create more opportunities for outdoor activities and exercise.

"Only a small proportion of adults are motivated to undertake [exercise] throughout the year, and the school curriculum allocates insufficient time for it," Hillman wrote.

"The source of the problem is that on average over the year only one or two of our waking hours in the mornings are spent in darkness whereas nearly half of the 10 to 11 waking hours after midday are in darkness. The critical limiting factor is obviously the onset of dusk."

He continued, "As most children are restricted from going out after dark, the lighter evenings would enable parents to let them spend more time outdoors. A significant majority of older people impose a curfew on themselves, preventing them from going out after dark, owing to anxiety about assault, and poorer vision and hearing."

Hillman argued that adding one to two hours of daylight in the evening would more than compensate for the hour lost in the morning. In an e-mail to MedPage Today, he pointed out that, for more than half the year, most people would still be asleep during that hour of extended darkness.

Some U.S. physicians contacted by MedPage Today and ABC News indicated that Hillman's proposal has some merit.

Phyllis Zee, MD, a sleep researcher at Northwestern University in Evanston, Ill., said in an e-mail that exposure to bright light is well known to improve well-being in several ways.

"As far as exercise -- less clear -- because as we all know, even in the summer many people do not engage in regular exercise. However, it will certainly allow more opportunity to exercise and enhance ability to engage in both social and physical activities," she wrote.

Similarly, Adam Rindfleisch, MD, a family medicine specialist at the University of Wisconsin, called the idea "intriguing and certainly worth exploring."

But he cautioned that putting more daylight into the evening would not necessarily translate into more outdoor exercise, a point made bluntly by another researcher as well.

Hillman's proposal "assumes that a lack of daylight is somehow a barrier to exercise. I don't know of any evidence for that," scoffed Goutham Rao, MD, clinical director of the Children's Hospital of Pittsburgh's weight management clinic.

"Americans have plenty of opportunity to exercise indoors, where daylight is less of an issue," Rao said in an e-mail.

Studies in the medical literature have yielded conflicting verdicts on whether daylight saving time has health benefits.

Most research has focused on the short-term effects of resetting the clocks. Several studies have found increases in traffic accidents and workplace injuries the Monday after the spring implementation of daylight saving time. Researchers have blamed sleep loss associated with the hour cut from Sunday morning.

But when a Canadian scientist presented one such study in a letter to the New England Journal of Medicine in 1996, it drew several critical responses -- including one from a researcher at the U.S.-based Insurance Institute for Highway Safety, who cited other studies indicating a net reduction in car crashes during daylight saving time.

Only a handful of studies have addressed the longer-term health effects of rescheduling sunrise and sunset. One of the largest and most rigorous was published in 2003 in the Journal of Psychosomatic Research by Henry Olders, MD, of McGill University in Montreal.

Olders analyzed data on affective disorder prevalence collected in the EURODEP and the Epidemiologic Catchment Area studies, involving nine European and five U.S. cities, respectively. The prevalence figures varied by twofold within these studies, which Olders said defied explanation.

He found that the average sunrise time in these cities correlated significantly with prevalence of depression and dysthymia in the two studies, with Pearson values ranging from -0.629 to -0.892 (P<0.05). In the article, he suggested that year-round daylight saving time could reduce the prevalence of these disorders.

Olders told MedPage Today in an e-mail that Hillman's hypothesis regarding exercise was credible, and could explain the findings from his own study.

"A contributor to the lower rates of depression seen in cities with later sunrise times could be a greater amount of exercise, as exercise is known to have an antidepressant effect. It could even be that the exercise effect is more important than the effect of rising times on depression rates," Olders said.

He added that it would be relatively easy to conduct a large-scale trial measuring physical activity with accelerometer-equipped devices -- which could include newer cell phones -- to determine if daylight saving time had an effect.

Hillman estimated that the year-round, enhanced daylight saving time would provide an extra 300 hours of useable daylight annually for adults and 200 more for children, assuming a longer sleep period for them.

"Adopting this proposal for a clock change is an effective, practical, and remarkably easily managed way to better align our waking hours with the available daylight during the year," he wrote in BMJ.

One criticism is that, at higher latitudes, sunrise in December and January could come well after 9:00 a.m. under the scheme.

Hillman told MedPage Today that these late sunrises "would occur for a very short period of the year."

He said the benefit would be greatest around the spring and fall equinoxes rather than during high summer when, he acknowledged, "there is already more than adequate daylight and sunlight."

"The attractions of more 'accessible' daylight hours would be appreciated not only after coming home from work and school but also at weekends," Hillman said.

"The waste of these hours is accounted for by the fact that the great majority of the population get up well after sunrise for most of the year but are then denied opportunities for daylight-dependent activities in the latter part of the day owing to the onset of dusk," he argued.

But Rindfleisch at the University of Wisconsin questioned the assumption that time spent indoors is a "waste."

"If more sunlight equates to more 'doing" as opposed to reflecting or stopping to simply be, which has traditionally been a piece of the winter experience, will we lose something?"

This article was developed in collaboration with ABC News.