Studies conducted over two decades revealed that individuals who consumed more caffeine through tea or coffee experienced improved physical function as they aged. The data collection process included over 12,000 individuals between 45-74 years who were followed for 20 years after initial enrollment in the study.

Individuals were interviewed using a structured questionnaire between 1993 and 1998 for the first time at midlife age of 53 on average.

At these interviews, individuals were queried on their consumption of beverages containing caffeine such as soft drinks, tea and coffee; their portion sizes and frequency of eating food with caffeine such as chocolate.

Information was also provided regarding sleep duration, physical activities, dietary habits, height and weight measurements, medical history records and sociodemographic traits.

Between 2006 and 2010, participants in the second follow-up interviews were required to record their weight as well as other information. At their third follow-up interviews between 2014 and 2017 (when on average individuals were aged 73 years), individuals were again asked to document their weight as well as respond to an additional question: “Are You Feeling Full of Energy?”

Handgrip strength was evaluated, as was the time it took to complete a timed up-and-go test (TUG). Physical frailty was defined as having at least two of four factors outlined: 1. Weight loss defined as over 10% between the second and third follow-up visits.
2. Exhaustion defined as yes answers from questionnaires umplut 3. Slowness defined as slowest TUG quintile.
4. Weakness can be defined by using quintile strength measurements of handgrip strength as a yardstick.

Tea and coffee were the primary sources of caffeine consumption among these participants, accounting for 12.1 and 84.4 of total consumption respectively. Of all participants who consumed caffeine every day, 68.5% consumed coffee on an everyday basis; 52.9% of this group drank one cup, 42.2 consumed two or three cups daily and 4.9% had four or more.