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- Cho, E, et al.
(författare)
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Dairy foods, calcium, and colorectal cancer : A pooled analysis of 10 cohort studies
- 2004
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Ingår i: Journal of the National Cancer Institute. - Harvard Univ, Sch Med, Channing Lab, Boston, MA 02115 USA. Brigham & Womens Hosp, Dept Med, Channing Lab, Boston, MA 02115 USA. Harvard Univ, Sch Publ Hlth, Dept Nutr, Boston, MA 02115 USA. Harvard Univ, Sch Publ Hlth, Dept Epidemiol, Boston, MA 02115 USA. Harvard Univ, Sch Publ Hlth, Dept Biostat, Boston, MA 02115 USA. Loma Linda Univ, Ctr Hlth Res, Sch Med, Loma Linda, CA USA. Maastricht Univ, Dept Epidemiol, Maastricht, Netherlands. Harvard Ctr Canc Prevent, Boston, MA USA. Univ Minnesota, Sch Publ Hlth, Div Epidemiol, Minneapolis, MN 55455 USA. SUNY Buffalo, Dept Social & Prevent Med, Buffalo, NY USA. TNO, Nutr & Food Res Inst, Dept Epidemiol, Zeist, Netherlands. Univ Toronto, Fac Med, Dept Publ Hlth Sci, Toronto, ON, Canada. Natl Publ Hlth Inst, Dept Epidemiol & Hlth Promot, Helsinki, Finland. Fred Hutchinson Canc Res Ctr, Canc Prevent Res Program, Seattle, WA USA. Albert Einstein Coll Med, Dept Epidemiol & Populat Hlth, Bronx, NY 10467 USA. Natl Inst Environm Hlth Sci, Epidemiol Branch, Res Triangle Pk, NC USA. NYU, Dept Obstet Gynecol, Sch Med, New York, NY USA. Natl Inst Environm Med, Div Nutr Epidemiol, Stockholm, Sweden. NYU, Sch Med, Nelson Inst Environm Med & Kaplan Canc Ctr, New York, NY USA. : OXFORD UNIV PRESS INC. - 0027-8874 .- 1460-2105. ; 96:13, s. 1015-1022
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Tidskriftsartikel (refereegranskat)abstract
- Background. Studies in animals have suggested that calcium may reduce the risk of colorectal cancer. However, results from epidemiologic studies of intake of calcium or dairy foods and colorectal cancer risk have been inconclusive. Methods: We pooled the primary data from 10 cohort studies in five countries that assessed usual dietary intake by using a validated food frequency questionnaire at baseline. For most studies, follow-up was extended beyond that in the original publication. The studies included 534 536 individuals, among whom 4992 incident cases of colorectal cancer were diagnosed between 6 and 16 years of follow-up. Pooled multivariable relative risks for categories of milk intake and quintiles of calcium intake and 95% confidence intervals (CIs) were calculated. All statistical tests were two-sided. Results: Milk intake was related to a reduced risk of colorectal cancer. Compared with the lowest category of intake (<70 g/day), relative risks of colorectal cancer for increasing categories (70-174, 175-249, and greater than or equal to250 g/day) of milk intake were 0.94 (95% CI = 0.86 to 1.02), 0.88 (95% CI = 0.81 to 0.96), and 0.85 (95% CI = 0.78 to 0.94), respectively (P-trend<.001). Calcium intake was also inversely related to the risk of colorectal cancer. The relative risk for the highest versus the lowest quintile of intake was 0.86 (95% CI = 0.78 to 0.95; P-trend = .02) for dietary calcium and 0.78 (95% CI = 0.69 to 0.88; P-trend<.001) for total calcium (combining dietary and supplemental sources). These results were consistent across studies and sex. The inverse association for milk was limited to cancers of the distal colon (P-trend<.001) and rectum (P-trend = .02). Conclusion: Higher consumption of milk and calcium is associated with a lower risk of colorectal cancer.
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| 3. |
- Cho, K. B., et al.
(författare)
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The substrate reaction mechanism of class III anaerobic ribonucleotide reductase
- 2001
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:27, s. 6445-6452
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Tidskriftsartikel (refereegranskat)abstract
- The substrate mechanism of class III anaerobic ribonucleotide reductase has been studied using quantum chemical methods. The study is based on the previously suggested mechanism for the aerobic class I enzyme, together with the recently determined X-ray structure of the anaerobic enzyme. The initial steps are similar in the mechanisms of these enzymes, but for the suggested rate-limiting steps there are key differences. In the class I enzyme, the 3 ' -keto group of the substrate is protonated in a step involving formation of a sulfur-sulfur bond between two cysteines, One of these cysteines is not present in the anaerobic enzyme. Instead, carbon dioxide is formed in this step from formate, which is present as a cofactor. In line with previous suggestions from experimental observations, the formate first forms a formyl radical. The next step, where the formyl radical protonates the 3 ' -keto group of the substrate, is suggested to be rate limiting with a calculated total barrier of 19.9 kcal/mol, in reasonable agreement with the experimental rate-limiting barrier of 17 kcal/mol. Zero-point and entropy effects are found to be quite significant in lowering the barrier. The mechanism for the entire cycle is discussed in relation to known experimental facts.
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