A new study has shown that elderly men with higher activity of the hormone IGF-1, or insulin-growth factor, appear to have greater life expectancy and reduced cardiovascular risk.
IGF-1, a hormone similar in molecular structure to insulin, is released from the liver and plays a significant role in childhood growth and continues to have anabolic effects in adults.
For the study, researchers evaluated 376 healthy elderly men between the ages of 73 and 94 years.
A serum sample was taken from each participant at the beginning of the study and researchers were contacted about the status of the subjects over a period of eight years.
The study showed that subjects with the lowest IGF-1 function had a significantly higher mortality rate than subjects with the highest IGF-1 bioactivity.
These findings were especially important for individuals who have a high risk to die from cardiovascular complications.
These new findings come as a result of a new form of testing for IGF-bioactivity.
In this study, researchers used a new method, a bioassay, to measure the function of IGF-1 in the blood.
Contrary to commonly used methods to measure IGF-1, the IGF-1 bioassay gives more information about the actual function (bioactivity) of circulating IGF-1 in the body.
"The bioassay allowed us to more clearly see the association between high circulating IGF-1 bioactivity and extended survival," said Michael Brugts, MD, of the Erasmus Medical Center in Rotterdam, The Netherlands and lead author of the study.
"Interestingly, we could not find such a relationship when IGF-1 in blood was measured with the more commonly used methods," he added.
Immunoassays, commonly used previously to determine IGF-1 circulation levels, remove certain proteins that interfere with accurate measurements. Recent studies however have found that these proteins are important modulators of IGF-1 bioactivity.
The bioassay used in this study does not disregard or remove this protein, thus enabling researchers to have a more accurate understanding of IGF-1 function.
Brugts said that determination of IGF-1 function using the bioassay opens the possibility to gather new insights about the functions of IGF-1 in the body.
The study is published in the Journal of Clinical Endocrinology and Metabolism (JCEM).