Probing the Relationship Between Declining Renal Glomerular Filtration Over the Life Span and General Biological Aging: Does the Former Provide Means to Estimate the Latter?

While a consistent, gradual decline in the renal glomerular filtration rate (GFR) is a characteristic occurrence over the human life span, the exact pathophysiology behind this event remains unresolved. Evidence to date suggests that the endogenous glucose-insulin system could be involved at some level. Diabetic-induced nephropathy, one of the most prevalent chronic renal diseases, is closely linked to a severe form of insulin resistance (IR). Nevertheless, it is less certain that the ubiquitous milder forms of IR in nondiabetics ascribed customarily to routine, poor choices in diet and exercise management can over time diminish GFR and adversely influence other renal functions to any perceptible extent. Baseline data for cross-sectional analyses were obtained from a cohort of healthy, nondiabetic volunteers (fasting blood glucose [FBG] ≤ 125 mg/dL) involved in prior clinical studies. Slope-based rather than threshold analyses were mainly employed. These measurements were applied for the most part to correlate age, FBG levels used as an estimate of IR activity, and systolic blood pressure (SBP) to a variety of metabolic parameters during aging with a primary focus on GFR. Considering cause and effect, FBG and SBP correlate positively with the diminishing GFR over a major part of the life span. The decline in GFR begins somewhere around the mid-20s and coincides with key temporal increases in FBG and SBP levels. A close time-based setting suggests that IR plays a prominent role in the declining GFR that occurs over the life span. This is perhaps due in part through deleterious effects of rising levels of insulin, glucose, and SBP individually or combined that are also popular proposed causative factors for human aging in general. On the philosophical side, the latter fact suggests that the declining GFR might provide a practical way to estimate the rate of overall human biological aging.