SEATTLE — Soon it will be that sad time again, when thoughts turn from turkey and trimmings to trimming down in the new year: Weight loss is on the horizon for many, and nutritional supplements may help midlifers control the pounds, say Seattle researchers.

Middle-aged people who are obese or just overweight might benefit from taking chromium, vitamin B6, vitamin B12 or a multivitamin, scientists at the Fred Hutchinson Cancer Research Center found in one of the largest studies of how supplements may affect weight.

All four of the supplements "had significant, consistent relationships with weight control," said M.C. Nachtigal, lead author of the research that looked at 10-year use of the pills by more than 15,500 study participants.

Weight loss was not great among those who took the vitamins or chromium. The effects had more to do with controlling weight during middle age, when most people put on the pounds.

Chromium came out best among the supplements, the researchers found.

Obese men who took relatively high daily doses (more than 150 milligrams) of the mineral lost an average of about 3 pounds. Obese women gained only about 3 pounds.

But over a decade, people who consistently took any of the four supplements, either in high or low doses, consistently gained less than those who took none. For each substance, they gained from 2 to 17 fewer pounds than those who took none.

Overweight men who took five or more multivitamin pills a week, for example, gained an average 11.5 pounds, compared with 13.8 pounds for those who took none. Overweight women taking the same amount gained an average 17.7 pounds, compared with 20.7 pounds for those who took none.

More than two-thirds of the U.S. population aged 55 to 74 is overweight or obese, experts say. Most weight-loss efforts are focused on diet and exercise. But millions use supplements. One study, for example, found that one-third of dieters used supplements.

The Hutchinson scientists analyzed 15,665 questionnaires returned by residents, average age 55, of 13 Washington state counties. All are participating in a larger, ongoing study of the effects of supplement use on cancer risk.

The Hutchinson research, reported in the October edition of the Journal of Alternative and Complementary Medicine, also examined the use of 10 other supplements: coenzyme Q10, dehydroepiandrosterone, essential fatty acids, fiber, garlic, ginkgo, ginseng, melatonin, soy and St. John's wort. None had a significant impact on weight control.

Nachtigal and her colleagues said they don't know whether the B vitamins, multivitamins and chromium actually prevented weight gain or aided weight loss. More research is needed to explore that question, they said.

The researchers could only speculate about how the supplements might act to control weight. But other, smaller studies also have suggested chromium might help keep off the pounds. It helps keep blood sugar at an appropriate level; low blood sugar stimulates appetite. The vitamins are known to help control the use of calories and energy.

A limitation of the Hutchinson study is that it relied on respondents' memories of how much and when they took the supplements. The scientists said future research should have "randomized trials" in which the doses are monitored. The study also was limited by the fact that 93 percent of the respondents were white.

Still, Nachtigal said, the study was a good beginning to learning more about how supplements might affect weight.

"It's like a broad overview to see what's out there," she said. "It gives direction for further research."