Insulin-like Growth Factor I Levels and Heart Failure Risk in Older People

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The summary below is from the full report titled "Serum Insulin-like Growth Factor I and Risk for Heart Failure in Elderly Individuals without a Previous Myocardial Infarction: The Framingham Heart Study." It is in the 21 October 2003 issue of Annals of Internal Medicine (volume 139, pages 642-648). The authors are R.S. Vasan, L.M. Sullivan, R.B. D'Agostino, R. Roubenoff, T. Harris, D.B. Sawyer, D. Levy, and P.W.F. Wilson.

What is the problem and what is known about it so far?

Insulin-like growth factor I (IGF-I) is a substance similar to insulin. It stimulates cell growth and may inhibit cell death in many body tissues and organs. It affects the heart in several ways. It can increase the size of heart muscle and the ability of the muscle to contract and pump blood. It also may reduce cell death when poor or absent blood flow (ischemia) or toxins injure heart muscle.

Heart failure is an inability of the heart muscle to pump blood normally. It is a serious condition that occurs more commonly in older adults than in middle-aged adults. As people age, levels of IGF-I in the blood decrease. Because low levels of IGF-I may adversely affect the heart and because the incidence of heart failure increases as people age, researchers wonder whether low levels of IGF-I are a risk factor for heart failure.

Why did the researchers do this particular study?

To see whether low levels of IGF-I are associated with increased risk for heart failure in older adults.

Who was studied?

717 older people from Framingham, Massachusetts. Their average age was 78 years.

How was the study done?

The researchers began following people living in Framingham in 1948. Every 2 years, they interviewed and examined participants and reviewed medical records. In this study, the researchers include only participants who were alive in the early 1990s and did not have a heart attack or heart failure. The researchers obtained blood samples from these participants and measured serum IGF-I levels. They continued following the participants for 5 to 9 more years. They then examined whether people who developed heart failure had lower levels of IGF-I than did people without heart failure. To ensure that observed relationships were not due to factors other than IGF-I levels, they did analyses that "controlled for" other factors, such as high blood pressure, diabetes, and high cholesterol, which might be associated with increased risk for heart failure.

What did the researchers find?

During follow-up, 56 people developed heart failure. Participants with lower levels of IGF-I developed heart failure more often than did those with higher levels.

What were the limitations of the study?

Participants were healthy, elderly white adults from the northeastern United States. Findings might differ in other racial or ethnic groups, in people 50 to 70 years of age, and in sicker patients. Serum total rather than biologically active free IGF-I levels were measured. Increased heart failure risk may be more closely associated with low levels of active free IGF-I than with serum total IGF-I.

What are the implications of the study?

Low levels of serum IGF-I are associated with increased risk for heart failure in older people. Of note, high levels of IGF-I are associated with increased risk for cancer. Future research should confirm associations and carefully explore the efficacy and safety of increasing IGF-I levels in people at high risk for heart failure.