Incidence of colorectal cancer in relation to glycemic index and load in a cohort of women.
BACKGROUND
Dietary glycemic index (GI) and glycemic load (GL) affect circulating insulin concentrations. Elevated circulating insulin concentrations can increase insulin-like growth factor-1, and both of these hormones may have growth-promoting effects within the colorectum.


METHODS
We examined associations of GI and GL with colorectal cancer (CRC) among participants in the Iowa Women's Health Study (n = 35,197; ages 55-69 years at baseline in 1986). Over 15 years of follow-up, we identified 757 cases of colon cancer and 209 cases of rectal cancer (954 CRC cases).


RESULTS
Overall, neither GI nor GL were significantly associated with incident CRC. However, among obese women (baseline body mass index >/=30 kg/m(2)) CRC incidence was increased in the highest versus lowest quintiles of GI (relative risk, 1.66; 95% confidence intervals, 1.13-2.43; P for trend = 0.02) and GL (relative risk, 1.79; 95% confidence intervals, 1.19-2.70; P for trend < 0.01). This pattern of increased risk for obese women with high GI or GL tended to hold for both colon cancer and rectal cancer, and for nondiabetic women as well. No statistically significant associations were observed between GI or GL and CRC among subjects whose baseline body mass index was <30 kg/m(2).


CONCLUSIONS
Our findings suggest that high GI or GL are not major CRC risk factors among older women in general, but may increase CRC risk among women who are obese.
McCarl
Mary
M
Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Suite 300, 1300 South Second Street, Minneapolis, MN 55454-1015, USA.
Harnack
Lisa
L
Limburg
Paul J
PJ
Anderson
Kristin E
KE
Folsom
Aaron R
AR
D000368:Aged; D015992:Body Mass Index; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D005247:Feeding Behavior; D005260:Female; D038321:Glycemic Index; D006801:Humans; D015994:Incidence; D007484:Iowa / Q000453:epidemiology; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000453:epidemiology; D015995:Prevalence; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors; D011795:Surveys and Questionnaires
D004040:Dietary Carbohydrates