IGF I and II are proteins in the body that help to regulate growth and development in early life, and are also thought to be important for adult health.
Researchers from the Medical Research Council (MRC) Unit for Lifelong Health and Ageing at UCL, analysed information on more than 1,500 men and women taking part in the MRC National Survey of Health and Development, which follows people born across England, Scotland and Wales in 1946. Individuals’ IGF I and II levels were taken from blood samples collected at ages 53 and 60-64. The researchers related these to how much fat and lean (muscle) mass participants had at age 60-64, adjusting for the person’s height.
Around two thirds experienced an apparent decline in their IGF I and II levels between their early 50s and early 60s. IGF-I levels decreased by nearly 13 per cent, on average, and IGF-II levels dropped by an average of 12.5 per cent.
Those who experienced larger declines in IGF I and II during this time also had higher fat mass at age 60-64, compared with those who experienced lesser or no decline. However, reduced levels of IGF I and II did not appear to be related to lean mass. This contradicts the idea that declines in IGF I and II lead to lower muscle mass levels in old age.
“More research is needed to better understand the roles that IGF I and II play in regulating fat mass in adults,” explained David Bann, lead author, “particularly given the difficulty of establishing cause and effect when using observational studies”.
Although the researchers suggested that using pharmacological supplementation of IGF (or growth hormone) to lower fat levels was “unlikely to be warranted given increases in cancer risk”, the findings suggest that “behavioural or early life interventions (such as improving exercise levels and diet) could potentially lessen the decline in IGF I and II with age, and in turn help limit build-up of body fat during this stage of life.”
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Changes in Insulin-Like Growth Factor-I and –II Associated with Fat but not Lean Mass in Early Old Age, by David Bann et al. was published in the Obesity in February 2015.