George R. Merriam of the University of Washington/VA Puget Sound Health Care System, who led the American study, tested an oral drug called capromorelin by Pfizer Global Research and Development that increases secretion of growth hormones.

Growth-hormone secretion and age are inversely related, Merriam said, such that a 60-year-old produces growth-hormone levels that would qualify as severely deficient for someone who is 20. Researchers noticed that much age-related decline is similar to the effects of growth-hormone deficiency, notably the decrease of muscle mass, strength and exercise capacity.

Placebos and various doses of the medicine were given to a group of 395 men and women aged 65-84 with mild physical limitations. All dosage levels caused an increase in growth-hormone secretion that was sustained for a 12-month testing period.

Subjects receiving the hormones gained an average of about 3 pounds of muscle mass. In six months participants could walk at a significantly quicker pace, and after 12 months they could climb stairs at about a 10-percent faster rate than at the outset of the study.

Tests for a similar drug by Merck show comparable changes in body composition to the Pfizer study, Merriam said.

Subjects in Merriam's study received varying dosages of capromorelin, with higher dosages producing greater effects, Merriam said. However, he added, in many cases the difference in the drug's effect on physical function was insubstantial between the lowest dose and the highest.

Growth hormones can cause insulin resistance, Merriam said, and can place patients at risk for diabetes, though none of the subjects in his test developed the condition. He also noted that the drug may cause mild negative effects on sleep and that testing would need to occur with much larger groups before the Food and Drug Administration would approve the medicine.

The Polish study focusing on the protein adiponectin was led by Agnieszka Baranowska-Bik from the Medical Center of Postgraduate Education in Warsaw.

The study involved 133 women aged 20 to 102, including 25 centenarians who were found to be healthier in some respects than younger obese participants.

The oldest women had significantly higher levels of adiponectin in their blood stream than the other age groups. Compared to a group of obese women, the centenarians displayed fewer signs of high blood pressure and metabolic syndrome, which involves obesity, insulin resistance (for which higher levels of insulin are needed to perform the hormone's regular functions), diabetes and the formation of fatty deposits.

Adiponectin helps prevent fatty deposits from forming in blood vessels and has anti-inflammatory properties. Low levels of the protein are thought to contribute to metabolic syndrome. Exercise and proper diets help increase levels of adiponectin, Baranowska-Bik said.

Despite the encouraging conclusions of the two studies, Merriam says that the day when people can pop an anti-aging pill with breakfast is distant.

"I'm an optimist," he said. "I just recognize that there are many steps along the way."

The studies were reported at the 6th International Congress of Neuroendocrinology in Pittsburgh.

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