G. Corrao et al., EXPLORING THE ROLE OF DIET IN MODIFYING THE EFFECT OF KNOWN DISEASE DETERMINANTS - APPLICATION TO RISK-FACTORS OF LIVER-CIRRHOSIS, American journal of epidemiology, 142(11), 1995, pp. 1136-1146
The analysis of the combined effects of nutritional factors with other
putative disease determinants in log-linear or logistic models is met
hodologically complicated by the strong multicollinearity between nutr
itional factors, resulting in poor precision in estimating the paramet
ers. Furthermore, the generally used multiplicative structure is not a
lways the most appropriate for describing the resulting joint effect o
f two or more factors on the disease risk. The authors addressed such
problems in a case-control study assessing the interactions between al
cohol intake, chronic hepatitis C virus (HCV) infection, and nutrient
intake on the risk of liver cirrhosis. During the period from November
1989 to May 1990, 282 patients admitted to the medical departments of
the hospitals of the Province of L'Aquila (central Italy) were enroll
ed: 115 cirrhotic patients aged 24-82 years (78 of whom were males) ho
spitalized because of liver decompensation, and 167 control patients a
ged 25-84 years (100 of whom were males) admitted to the same hospital
s for acute diseases unrelated to alcohol intake, infection with hepat
otropic viruses, and nutrition. No dose-effect relation was found betw
een the intake of any nutrient and the risk of cirrhosis using classic
al methods, The analysis of principal components showed, however, that
a pattern of higher lipid but lower protein and carbohydrate intakes
was significantly associated with the risk of cirrhosis. The Breslow a
nd Storer parametric family of relative risk functions showed that a m
ultiplicative structure was the most adequate to describe the joint ef
fect of nutritional pattern with alcohol intake and/or chronic HCV inf
ection, whereas an additive structure best described the joint effect
of chronic HCV infection and alcohol intake. In conclusion, the analys
is of principal components and the Breslow and Storer family are usefu
l tools to explore the role of diet on disease risk when precise patho
genic knowledge is not available. As an original finding, the authors
suggest that a higher lipid intake, combined with lower protein and ca
rbohydrate intakes, modifies multiplicatively the risk of cirrhosis as
sociated with alcohol intake and/or chronic HCV infection.