SAN DIEGO—Growth hormones commonly used by older men may raise cancer mortality risk significantly.


These hormones stimulate the liver to produce insulin-like growth factor-I (IGF-I), and a study suggests that higher serum IGF-I levels in older men may be associated with increased risk of cancer death independent of age, adiposity, and lifestyle.

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“This is one of the few studies that have examined this association,” said lead researcher Jacqueline Major, a doctoral student at the University of California in San Diego. “If future studies confirm our results, we would need an intervention study to see if lowering IGF-I to normal levels can reduce cancer events.” She reported findings here at the American Association for Cancer Research annual meeting.


Previous studies have explored the relation of IGF-I and cancer incidence, but few have actually looked at the association between IGF-I and cancer mortality, Major said. Previously published studies suggest that higher serum IGF-I is associated with in-creased risk of some common cancers, including prostate and breast cancer. She and her colleagues studied the association between serum IGF-I levels and all-cancer mortality in older community-dwelling men.


The researchers used data from a prospective population-based study of 633 men aged 50 and older (Rancho Bernardo Study). The mean age of the men was 73 years and all the men had serum IGF-I measured in 1988-91. The men were followed up through July 2006. The median IGF-I level was 96 ng/mL at baseline.


During the 18-year follow-up, 74 men (20% of the total deaths) died from cancer. Adjusted Cox regression analyses showed a significant relationship between IGF-I levels and all-cancer mortality. Higher IGF-I levels were associated with increasing risks of cancer death after adjusting for age, IGF binding protein-1, adiposity, alcohol consumption, current smoking, physical activity, and previous cancer. The mean BMI for these men was 26 kg/m2 and 9% of them were current smokers.


Men with the highest IGF-I levels had a 2.6 times higher adjusted risk of cancer death; the risk was nearly twofold greater for men with IGF-I levels above 100 ng/mL compared with men with lower levels.


“Our results are not definitive and must be confirmed in larger, ethnically-diverse populations. If confirmed, we need to be cautious when using growth hormones for children who are GH deficient,” Major said.


“Also, there are people who are using recombinant IGF-I for diabetes treatment. We may need to monitor IGF-I levels to make sure they don’t exceed certain levels. And there may be concerns about baby boomers who use growth hormones off-label for ‘anti-aging’ purposes.”