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Table 1 Characteristics of the included studies

From: Association between telomere length and the risk of colorectal cancer: a meta-analysis of observational studies

Author, publication yr, [Ref no] Country Site Study year Design Pros/retro Case selection Control selection Sample size_case/control Matching Male% Mean age ± SDb DNA source Measurement technique Adjusted factorsd Estimate of risks Remarks
Zee, 2009 [22] USA 78.8% colon; 21.2%:rectum 1982 nested pros Ca (PHS cohort) healthy men 191/306 age ±2years, smk, follow-up length all males 60.5 ± 8.66 PBL qPCR BMI, al, ex 0.8 (0.55–1.16) 50.3%: with aspirin use
Lee, 2010 [23] USA 76.3% colon; 23.7%:rectum Dec 2005 nested pros Ca (WHS cohort) healthy women 134/357 age ±2years,smk, follow-up length all females 60.1 ± 8.68 PBL qPCR age, smk, BMI, colorectal polyp, al, ex, pmp, HRT 0.94 (0.65–1.37) 35.1% with HRT
Pooley, 2010 [24] UK CRC/ADC Jan 1998 -Dec 2003 nested pros Ca c (EPIC) healthy 185/406 age, gender female control 45–75 PBL qPCR study plate 1.13 (0.54–2.36)  
Pooley, 2010 [24] UK CRC/ADC March 2001-Feb 2004 CC retro Ca registry (SEARCH) healthy 2249/2161 age, gender female control 18–69 PBL qPCR study plate 3.14 (1.77–2.58)  
Cui, 2012 [25] China CRC Dec 1996- May 2000 nested pros Ca (SWHS) healthy 441/549 age, date, time a, meal, antibiotic, mp all females 58.5 ± 8.7 PBL qPCR age, date, time 1.56 (0.92–2.64) part of 74942 cohort
Pellat, 2013 [26] USA (Utah) CRC 1991-94 CC (DALS) retro Ca (DALS) driver license & social security lists 249/374 (1991-94) (colon) 276/372 (1997–2002) (rectal) age, sex 54% 30–79 Cell line (colon), PBL (rectal) qPCR age, sex, BMI, smk, aspirin/NSAID, trans-fatty acid intake 0.96 (0.82–1.0) 44% on HRT, h/o aspirin, smk
Boardman, 2014 [27] USA colon polyps & CRC 2000+ CC retro Ca registry & Ca (Mayo biobank) healthy f 598/2212 age, gender, location. 47% (colon); 58% (Mayo) 48 (19–69) PBL qPCR multiple 3.53 (1.35–9.24) chemoradio Rx; naive Ca
Qin, 2014 [28] China CRC Jan 2007- Dec 2010 CC retro Ca, hospitalised unrelated healthy e 628/1256 age ± 5 years, gender 54.1% 58,8 ± 11.8 PBL qPCR smk, Al, age, sex. 1.47 (1.09–1.99) chemo-radio Rx & radio Rx; naive Ca
  1. a matched with date and time of sample collection; b: mean age of cases: c: cancer free at the baseline assessments, but diagnosed as CRC at least 6 months after; ****: overall from 3 sources; *****: CRC & without CRC; Al alcohol use, BMI body mass index, Ca cancer, CRC colorectal cancer, CC case-control study design, healthy healthy controls, h/o history of; nested: nested case-control study, HRT hormone therapy, mp menopause, mth months; nested: nested case-control, PHS prospective physicians’ health study, qPCR quantitative PCR, EPIC European prospective investigation into cancer, PBL peripheral blood leucocyte, pmp post menopause, Pop population, Ref Reference, smk smoking status, SWHS Shanghai women’s health study, d: further controlling factors to case-control status,e: based on authors address; f: unrelated residents; NA not available or not relevant, as appropriate, Rx treatment or therapy as appropriate