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A study on rhesus macaques funded by the National Institute on Aging was started in 1989 at the University of Wisconsin–Madison and is still ongoing. Monkeys were enrolled in the study at ages of between 7 and 14 years. Preliminary results published in 2000 showed lower fasting insulin and glucose levels as well as higher insulin sensitivity and LDL profiles, associated with lower risk of atherogenesis in dietary-restricted animals.[43] CR also attenuated age-related loss of muscle mass and function (sarcopenia) in these primates.[25][26] Results published in 2009 showed that caloric restriction in rhesus monkeys blunts aging and significantly delays the onset of age-related disorders such as cancer, diabetes, cardiovascular disease, and brain atrophy. 80% of the calorie-restricted monkeys were still alive, compared to only half of the controls.[44] [45] Results to date have also found a trend toward a reduced overall death rate, which has not yet reached statistical significance. An additional analysis, restricted to causes of death related to aging, did find a significant reduction in age-related deaths. However, the interpretation of this finding is uncertain, as it is hypothetically possible that the exclusion of deaths due to non-aging causes may somehow mask an involvement of CR in such deaths, although the sample size is too low to say for certain.[1][3] A study published in 2011 examined the effect of stress on various brain functions in these monkeys.[46] In the control group, stress reactivity was associated with less volume and tissue density in areas important for emotional regulation and the endocrine axis, including prefrontal cortices, hippocampus, amygdala, and hypothalamus. CR reduced these relationships. In contrast to the conclusions reached by the University of Wisconsin–Madison (WNPRC) study, a 2012 National Institute on Aging (NIA) study published in the journal Nature, concluded that a calorie restriction regimen did not improve survival outcomes whether implemented in young or older age rhesus monkeys.[47] A key difference between the WNPRC and the NIA studies is that the monkeys in the WNPRC study were fed a more unhealthy diet.[48] In 2006, researchers at New York's Mount Sinai School of Medicine reported results comparing the brains of 3 monkeys fed a normal diet and 3 monkeys on a CR diet for their entire lives. The normal diet group "consisted of three male Squirrel monkeys (20–27 years old), who died from congestive heart failure, liver failure or complications of intestinal bleeding, respectively; the weight at the time of death of the CON group ranged 526–866 g. The CR group consisted of 3 male Squirrel monkeys (15–20 years old) on CR diet for 14 to 18 years, who died from inanition, complications of bleeding or by complications from liver necrosis, respectively; the weight at the time of death of CR group ranged 526–813."[49] The squirrel monkeys on a lifelong calorie-restrictive diet were less likely to develop Alzheimer's-like changes in their brains.[49] |
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