Higher Levels of IGF-1 Are Associated With a Decreased Risk of Alzheimer's Disease



Among a sample of participants from the Framingham study, high levels of IGF-1 are linked to a lower risk of Alzheimer’s disease and subclinical brain atrophy.

SAN DIEGO—Dementia-free patients with high levels of insulin-like growth factor 1 (IGF-1) show a lower risk of developing clinical Alzheimer’s disease and subclinical brain atrophy, according to research presented at the 136th Annual Meeting of the American Neurological Association.

According to Andrew J. Westwood, MD, lead author and resident from the Department of Neurology, Boston University School of Medicine, researchers are actively investigating the methods by which IGF-1 may affect the brain. “We know IGF-1 shares the same molecular pathways as growth factors like brain-derived neurotrophic factor (BDNF), which is involved with plasticity and neurogenesis,” he commented. “Despite the ongoing research in this area, we still do not know exactly how IGF-1 brings about these actions.”

To explore the relationship between IGF-1 levels and risk of Alzheimer’s disease, Dr. Westwood and his colleagues conducted a prospective study of 648 Framingham study participants, 63% of whom were female, with a mean age of 79. The investigators assessed serum IGF-1 level in these participants and followed them from 1990 to 1994. Between 1999 and 2005, the 161 dementia-free survivors underwent brain MRI.

Alzheimer’s Disease and IGF-1 Levels
Overall, the investigators documented 105 cases of Alzheimer’s disease, following up with patients for a mean of nine ± 4 years. Mean IGF-1 levels among the participants were 143 ± 60 μg/L.

Dr. Westwood’s research group found a link between IGF-1 levels and risk of developing Alzheimer’s disease. Using multivariable models adjusted for age, sex, apolipoprotein E (APOE) status, plasma homocysteine, and waist-hip ratio, the investigators showed that each standard deviation increase in baseline IGF-1 was associated with a 23% lower risk of Alzheimer’s disease. Supporting these results, participants with IGF-1 levels in the lowest quartile had lower brain volumes (b ± SD = – 0.6 ± 0.28) cross-sectionally, as well as an 80% greater risk of being diagnosed with Alzheimer’s disease.

Lifestyle May Affect IGF-1 Levels

Prior studies have suggested that IGF-1 may serve as a biological link between lifestyle and risk of Alzheimer’s disease. “In general, exercise seems to increase IGF-1 levels regardless of gender or age,” said Dr. Westwood. However, “Much of the research has been done in animals, and there are limited data in humans. We really don’t know enough to say which type or duration of exercise is needed at this stage.”

Dr. Westwood added that although it is still too early to derive clinical recommendations from his research, “Healthy diet, lifestyle, and regular exercise are staple recommendations for a longer life, and I think this study reinforces this recommendation. In the future, there may be a time when monitoring levels of hormones like IGF-1 can be useful, just as cholesterol or blood sugar levels are routinely checked today. However, first we must see further investigation and also whether modifying these levels can make a clinical impact for patients.”

—Lauren LeBano

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