- Fluorescent supermarket lights can boost vitamin concentrations in vegetables../b]

- If you can't pick and eat your vegetables immediately, continuous light conditions could make them more nutritious. /b]

There might be a bright side to the harsh and unflattering lighting in most supermarkets: healthier veggies.

In a recent study, spinach gained nutritional value as it sat for days under fluorescent lights, with some vitamins doubling their concentrations. The discovery suggests that supermarkets and consumers might want to rethink the way they store their produce, said study author Gene Lester, a research plant physiologist at the United States Department of Agriculture in Beltsville, Md.

Continuous light exposure allows plants to maintain photosynthesis, Lester explained, and photosynthesis produces nutrients. Fluorescent supermarket lights, which mimic the spectrum of natural sunlight, are often kept on all the time, day and night.

"I was in the grocery store, and I happened to stop and think, 'Here's spinach in a clear, plastic box that can be exposed to light 24-hours a day, for two or three days before it's purchased,'" Lester said. That made him wonder: "Are we seeing a benefit after it's harvested?"

Lester chose to study spinach because it is one of the most nutritionally complete vegetables commonly available, with significant concentrations of vitamins C, A, K, E and folate. The plant provided Lester with the opportunity to look at a variety of nutrients at once.

Along with a colleague, Lester grew a variety of spinach plants under controlled conditions in the lab. They harvested the plants, then washed and separated the leaves, just like farmers and food distributors do. They tested some leaves right away for nutritional content.

They put the spinach in either brown bags or clear plastic boxes and waited for up to nine days before grinding up some leaves and testing them again. All leaves were kept at about 39 degrees Fahrenheit, the temperature of a typical supermarket refrigerator case.

After just three days, the scientists reported in the Journal of Agricultural and Food Chemistry that concentrations of some vitamins rose by between 10 and 20 percent. After nine days, folate and vitamin K levels had risen by as much as 100 percent. In covered spinach, nutritional content stayed the same or worsened over time.

Results varied somewhat depending on the type of spinach used. A flat-leafed variety, for example, tended to get limp after a while. Lester suspects that nonstop light exposure also benefits other fruits and vegetables.

To boost the nutritional content of spinach and other produce, Lester suggests that consumers select packages from the front of display cases that are kept under continuous light. Distributors could help by packaging spinach in long, shallow containers and putting labels on the side of the containers.

Despite the new findings, it's probably not necessary to examine the lighting conditions of your local market or to keep your fridge light on at all times, said Marion Nestle, a nutritionist at New York University and author of "What to Eat." Most Americans aren't vitamin-deficient.

Other studies have shown that light, heat and time deteriorate fragile nutrients, like vitamin C, she added, which is why orange juice containers are usually opaque. Veggies that have sat around for days or even weeks also generally don't taste that great.

"You want to buy fresh vegetables and eat them as close as possible to the time you buy them," Nestle said. "They taste better, and they are potentially better for you."