Physical and Cognitive:
Physical ability was assessed through self-report in 1997 and through both self-report and the measurement of performance in two physical tasks in 1999. The questions referred to the ability on the day of the interview. Research has shown that physical abilities can be reliably and validly assessed through self-report (23). The self-reported physical abilities were determined from 26 items including items from Katz index of activities of daily living (ADL) (24) as well as questions about demanding activities like running. This instrument has been validated in Denmark and shown to discriminate different levels of functional abilities among community-dwelling elderly (25). All items were rated on a 4-to-1 scale with response options ranging from "can do without fatigue" (4) to "cannot do" (1). To identify a quantitative subscale, the items were factor analyzed in the total twin sample from the 1995 survey (14). This identified two factors where the first factor loaded highest on items dealing with ability to walk, run, climb stairs, and carry weights and was interpreted to reflect a dimension of strength. The second factor loaded highest on items dealing with ability to wash, dress, and get in and out of bed and was interpreted to reflect a dimension of agility. Only the strength factor was used in this analysis due to little variability on the agility scale.

The strength scores from the 1997 and 1999 surveys were calculated by taking the average response of the 11 items identified to be relevant for this score. The factor has previously been found highly reliable for functional abilities (26). In the 1999 survey, three additional items dealing with endurance performance (self-reported walking, running, and cycling distance) were included. A composite score was calculated by taking the average response from these items.

In the 1999 survey, the participants were also invited to perform two tests of physical abilities: maximum handgrip pressure and the repeated chair stand test. The grip strength was measured by a hand dynamometer (Smedleys dynamometer TTM, Tokyo). The maximum value of three measures with each hand was used in the analyses. In the repeated chair stand test, the participants were asked to rise and sit five times from a chair as quickly as possible with their arms folded over their chest. The pulse was recorded immediately before and after the test. The test, which was timed, was stopped if five attempts were not successfully performed within 60 seconds.

The age was 78.2 with a standard deviation (SD) of 4.4 (females: 78.4 (4.6), males: 77.8 (4.0)). Sixteen (2.3 percent) participated in the interview through a proxy responder.

The cognitive functioning of the participants was assessed using the mini-mental state examination (MMSE), which was integrated into the interview.

Data Analyses:
ACE Genotype:
In all, 169 (24.7 percent) twins had the II genotype, 344 (50.3 percent) had DI, and 171 (25.0 percent) had DD genotype. The genotype frequencies in men and women, and in the age groups shown in Table 1, were in Hardy-Weinberg equilibrium (p > |0.3) and were highly comparable to proportions found in Danish populations in two previous studies (10, 28). The distribution of the ACE genotype in the MZ twins who were assigned to their co-twin's genotype did not differ from that of the other study subjects (results not shown).

Allele frequencies were computed from the genotype frequencies, and Hardy-Weinberg equilibrium was tested by a chi-square test with one degree of freedom. We compared the three ACE genotypes with regard to physical and cognitive abilities and other characteristics at baseline (1997 interview wave) and in 1999 at the second interview wave. Longitudinal changes in cognitive skills and physical abilities were examined for twins participating in both interview waves. Finally, we examined the influence of ACE-genotype on survival through linkage with mortality data for the entire cohort.

Continuous variables were compared using multivariate linear regression models, and categorical data were compared using logistic regression models controlling for the age of the participants. To account for the non-independence of the observationsprocessed text: