Dietary Acid Load, Kidney Function and Disability in Elderly

Physical decline and frailty result from age- and disease-related impairments in organs and tissues. Frailty research has focused on the musculoskeletal, neurological and circulatory systems; yet interventions targeting these systems had limited success in preventing and treating functional decline. Given the aging of the US population, additional avenues for intervention development are urgently needed. Fragility and disability in people ≥65 strongly correlate with declining kidney function and are evident even in early stages of chronic kidney disease (CKD). Moreover, CKD is highly prevalent in the elderly and associates with sarcopenia, osteopenia, and increased incidence of fractures/falls with hospitalization. Low serum bicarbonate and impaired acid-base homeostasis, also common in CKD, are increasingly appreciated as contributors to functional decline with advancing age. With aging, the adaptive response of the kidney to low serum bicarbonate and high metabolic acid load becomes maladaptive, facilitating CKD progression. Conversely, in adult patients with CKD, maintenance of serum bicarbonate at 24 meq/L with oral bicarbonate supplementation or increased consumption of base-forming foods slows CKD progression.

The study investigators propose the current study and protocol based on the evidence summarized above and our preliminary studies, which suggest that: In the Health Aging and Body Composition cohort (age 70-79) lower dietary acid load associates with stable kidney function over a 7-year follow-up, independent of age, race, gender, BMI, diabetes, hypertension or smoking status; metabolomics analysis in participants of the African American Diabetes Heart Study suggested that it is feasible to segregate a urine metabolomics profile in the early stages of CKD (stages 2 and 3), and that lower consumption of base-forming fruits and vegetables and higher rates of acid excretion may be associated with CKD and its progression.

The investigators therefore hypothesized that decreasing metabolic acid production by titrating dietary acid load may ameliorate the generally expected, age-related decline in kidney function, decrease loss of lean body mass, preserve physical function, and ameliorate disability. This is not a treatment study as the investigators are exploring the effects of bicarbonate on these age-related issues.

Inclusion criteria

• Age 65 +years of age
• Short physical performance battery (SPPB) score>3
• Estimated glomerular filtration rate (eGFR) 30-89
• Net endogenous acid production (NEAP) >=40 mEq/d
• Willing to provide informed consent and agrees to randomization
• Not involved in another intervention study

Exclusion criteria

• Uncontrolled (>160 mg/dl fasting blood glucose), insulin-dependent diabetes and/or uncontrolled hypertension (Systolic Blood Pressure >160, Diastolic BP>100)
• a current diagnosis of psychotic disorder
• take more than 14 alcoholic drinks per week
• plan to relocate out of the study area within the next year
• self-reported inability to walk across a room
• those who reside in nursing homes
• have difficulty communicating with study personnel due to speech or language or hearing problems
• had cancer requiring treatment in the past 1 year
• lung disease requiring regular use of corticosteroids or of supplemental oxygen
• cardiovascular disease (Class III or IV congestive heart failure)
• significant valvular disease, uncontrolled angina
• myocardial infarction, major heart surgery (i.e., valve replacement or bypass surgery) in past 6 months
• stroke, deep vein thrombosis, or pulmonary embolus in the past 6 months, Parkinson's disease or other progressive neurological disorder
• other medical or behavioral factors that in the judgment of the principal investigator may interfere with study participation or the ability to follow the intervention
• clinical judgment concerning safety or noncompliance
• Individuals with BMI <18.5; or weight loss >4% in last 6 months
• Montreal Cognitive Assessment (MoCA) score under 24
• End Stage Renal Disease (ESRD) on dialysis or primary kidney disease
• Other illness of such severity that life expectancy is less than 12 months
• Smoking; defined as not smoking for more than a year prior to the study
• Serum Bicarbonate (HCO3)>30 milliequivalents per liter (mEq/L); serum potassium out of normal range