Relationship between serum isoflavone levels and disability-free survival among community-dwelling elderly individuals: nested case-control study of the Tsurugaya project.
BACKGROUND
The longer healthy life expectancy observed in Japan may be partly attributed to the Japanese diet. The researchers sought to examine whether serum isoflavone levels are associated with disability and death.


METHODS
The researchers used a nested case-control study to compare serum isoflavones (daidzein, genistein, glycitein, and equol) levels between 165 participants that died or were certificated as disabled (cases) and 177 controls. Disability was defined by certification of long-term care insurance. Conditional logistic regression models were used to calculate the risk of isoflavones for the composite outcome.


RESULTS
The proportion of cases was lower in the group with the highest levels of equol (34/91, 37%) compared with equol nonproducers (84/161, 52%). The risk of disability or death among equol producers remained reduced after adjusting for age and sex (odds ratio: 0.55, 95% confidence interval: 0.33-0.93). In a multivariate model, this risk was also unchanged (odds ratio: 0.51, 95% confidence interval: 0.27-0.96). There were no significant associations between daidzein, genistein, and glycitein with the composite endpoint.


CONCLUSIONS
Higher serum equol levels, but not any other isoflavones, were inversely associated with the composite endpoint of disability and death. Although it cannot be concluded that equol per se has preventive effects on disability or death, higher equol levels appear associated with better health.
Department of Preventive Medicine and Epidemiology, Tohoku Medical Megabank Organization, Tohoku University, Sendai 980-8573, Japan. hozawa-thk@umin.ac.jp
Atsushi
A
Hozawa
Yumi
Y
Sugawara
Yasutake
Y
Tomata
Masako
M
Kakizaki
Toru
T
Tsuboya
Kaori
K
Ohmori-Matsuda
Naoki
N
Nakaya
Shinichi
S
Kuriyama
Akira
A
Fukao
Ichiro
I
Tsuji
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004185:Disability Evaluation; D006233:Persons with Disabilities / Q000706:statistics & numerical data*; D023381:Endpoint Determination; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D015577:Geriatric Assessment / Q000379:methods; D006801:Humans; D057187:Independent Living; D007529:Isoflavones / Q000097:blood / Q000145:classification; D007564:Japan / Q000453:epidemiology; D008017:Life Expectancy; D008136:Longevity / Q000502:physiology*; D008297:Male; D009026:Mortality; D016017:Odds Ratio; D048789:Phytoestrogens / Q000378:metabolism; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D012737:Sex Factors
D007529:Isoflavones; D048789:Phytoestrogens