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.
“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.”