Older adults typically do not drink later in the day to avoid the necessity of interrupting sleep to urinate. Sometimes they also limit ingestion of fluids to avoid the need to urinate when engaged in certain activities such as traveling or attending an event. Therefore, beverages that have greater fluid retention in the body leading to a more sustained positive hydration status could be advantageous in such situations. The composition of a beverage as well as other factors such as volume ingested and metabolism of components can affect the retention of the fluid in the body. Age may be another factor. The beverage hydration index (BHI), first described in 2016, was used to indicate the hydration response to thirteen well-known beverages in young male adults. The current study assesses the BHI of four beverages and how that response is affected by age following the standardized protocol. The four beverages have been chosen for inclusion in this study because they have been used by older adults to prevent dehydration.

Subjects sign an informed consent form and undergo a medical screening prior to participation. The screening includes a physical exam, anthropometry, chemical and lipid profiles, as well as measures of liver and renal function. The subjects are assigned to one of two groups based upon age.

Subjects participate in five experimental trials, one for each of the five beverages. The beverages are commercially-available and contain ingredients that are generally recognized as safe (GRAS). The order of the beverages is randomized. The list of ingredients on the bottle containing the beverage is obscured. The trials are identical and separated by at least five days. For each experiment, baseline measurements are conducted. Then the subjects consume one liter of the test beverage over thirty minutes. Additional measurements are performed thirty minutes post ingestion and then every hour for four hours post ingestion.

This study yields two BHI numbers for each beverage, one number for each study-group. The BHI numbers are indicative of the amount of fluid remaining in the body four hours after consumption of the beverage. The BHI number is inversely related to the amount of urine produced over the four hours. A greater BHI number indicates better fluid retention and maintenance of plasma volume.

Inclusion Criteria:

• 18-30 years or ≥60 years

Exclusion Criteria:

• cardiovascular, renal, or digestive diseases
• pregnancy
• breastfeeding
• smoking and/or use of nicotine-containing products
• illegal/recreational drug use
• medications that alter fluid balance (e.g., diuretics)
• allergy to Latex
• men with prostate issues that interfere with urination.

The ingredients-list is masked on the bottles of beverage. Test beverages are coded. The research nurse logs the code, administers the test beverage, and discards the empty bottle prior to the experiment and in the absence of the investigator and outcomes assessor. The investigator and outcomes assessor do not have access to the log. Subjects do not discuss the beverages with the investigator and outcomes assessor.