Prostate and colon cancer risks

[Guest guest]

Hi All,

See the pdf-availed below.

In the pdf, it is said:

" ...Body mass indices were calculated as [weight 5

years ago/(height 5 years ago)2 ].

2. American Cancer Society. Cancer Facts and Figures 2000. Atlanta:

Ameri-can

Cancer Society; 2000.

....The results from the medical factor stepwise logistic

regression model are presented in Table 4. Included in the

model were various medical conditions, both significant and

non-significant from the age-adjusted models in Table 3,

and factors that some others have found to significantly

increase risk (e.g., age, family history of prostate cancer, and

body mass index). ... "

What an unusual measure of body mass index?

There are other factors, such as inflammation, related to CRON that

are reported

to be not related to prostate cancer.

The use of the one population are good, but a prospective or

randomized control

study would be highly superior, in my estimation.

Ann Epidemiol. 2004 Oct;14(9):655-662.

Medical history, sexual, and maturational factors and prostate cancer

risk.

Lightfoot N, Conlon M, Kreiger N, Sass-Kortsak A, Purdham J,

Darlington G.

..... population-based study,

conducted from 1995 to 1999 in northeastern Ontario, used cancer

registry-identified cases (n=760), aged 45 to 84 years, diagnosed

between 1995

and 1998. Age-frequency matched controls (n=1632) were obtained from

telephone

listings.

... RESULTS: For the sexual-physical model,

marital status, family income, maximum height, number of marriages,

having

children, age at first marriage, birth, and needing to shave, and

acne were not

significantly related to risk. In the medical model, a family history

of

prostate cancer (OR, 2.99; 95% CI, 2.21-4.04) and history of venereal

disease

(OR, 2.12; 95% CI, 1.27-3.53) were associated with significantly

increased risk.

A history of allergies (OR, 0.78; 95% CI, 0.60-1.00), benign prostatic

hyperplasia (OR, 0.63; 95% CI, 0.49-0.81), and an annual physical

exam (OR,

0.43; 95% CI, 0.21-0.85) were associated with reduced risk. Other

factors

considered in the medical conditions model, body mass index, smoking

non-filter

cigarettes, and family income were not associated with prostate

cancer.

CONCLUSIONS: This study is consistent with other studies that suggest

that

infectious agents may be involved in prostate cancer development.

PMID: 15380796 [PubMed - as supplied by publisher]

The below to me certainly did appear to be of

sufficient relevance to CRON for colon cancer.

The contrast, for example, of the association of

physical activity with CRON variables versus

smoking strike me as notable.

See the pdf-available, as is reference 10, below.

Med Sci Sports Exerc. 2002 Jun;34(6):913-9.

Physical activity and colon cancer: confounding or interaction?

Slattery ML, Potter JD.

... a case-control study of colon cancer (N = 1993 cases and 2410

controls).

... RESULTS: No confounding was

observed for the physical activity and colon cancer association.

However,

differences in effects of diet and lifestyle factors were identified

depending

on level of physical activity. Most striking were statistically

significant

interactions between physical activity and high-risk dietary pattern

and

vegetable intake, in that the relative importance of diet was

dependent on level

of physical activity. The predictive model of colon cancer risk was

improved by

using an interaction term for physical activity and other variables,

including

BMI, cigarette smoking, energy intake, dietary fiber, dietary

calcium, glycemic

index, lutein, folate, vegetable intake, and high-risk diet rather

than using

models that included these variables as independent predictors with

physical

activity. In populations where activity levels are high, the estimate

of risk

associated with high vegetable intake was 0.9 (95% CI 0.6-1.3),

whereas in more

sedentary populations the estimate of risk associated with high

vegetable intake

was 0.6 (95% CI 0.5-0.9).

CONCLUSIONS: Physical activity plays an important role

in the etiology of colon cancer. Its significance is seen by its

consistent

association as an independent predictor of colon cancer as well as by

its impact

on the odds ratios associated with other factors. Given these

observations, it

is most probable that physical activity operates through multiple

biological

mechanisms that influence the carcinogenic process.

PMID: 12048315 [PubMed - indexed for MEDLINE]

...The proposed mechanisms between physical activity and

colon cancer include increased activity of free radical scav-enging

enzymes (3,6), improved immune function (15,27),

increased circulating T and B lymphocytes (14), reduced

body fat (12), increased gastrointestinal motility of colonic

contents (2), altered prostaglandin synthesis (24,25), altered

hormone levels (11), and regulation of insulin and triglyc-eride

levels (10). Some of these reports suggest that intense

levels of activity may have the greatest protective role with

cancer.

Confounding is defined as " a distortion in the estimated

exposure effect that results from differences in risk between

exposed and unexposed that are not due to exposure " (13).

For a variable to be considered a confounding variable, it

must be a risk factor for the disease among the nonexposed,

it must be associated with the exposure variable in the

population from which subjects arise, and it must not be in

the causal pathway from exposure to disease or affected by

exposure or disease. Determination of potential confound-ing

variables is not always easy, especially when there are

multiple hypothesized mechanisms, some of which may be

in the causal path. For instance, if physical activity is asso-ciated

with colon cancer through its ability to help maintain

body weight, adjustment for body mass index (BMI) would

be inappropriate. If however, physical activity acts through

other mechanisms, BMI may be an important confounding

variable because it is associated both with physical activity

and with colon cancer.

10. MCCARTY, M. F.

Up-regulation of IGF binding protein-1 as an

anticarcinogenic strategy: relevance to caloric restriction, exercise,

and insulin sensitivity.

Med. Hypotheses 48:297–308, 1997.

...The associations of various risk factors with risk of colon

cancer, given underlying levels of physical activity, show

that for many diet and lifestyle factors, associations are

stronger in populations that are more sedentary (Table 5).

The differences in association by underlying activity char-acteristics

are most notable for energy intake, dietary fiber,

vegetables, and overall high-risk dietary pattern where the

greatest effect is observed for those with low levels of

physical activity. On the other hand, cigarette smoking

appears to have a slightly greater influence among those

with higher levels of physical activity.

DISCUSSION

These data suggest that the physical activity and colon

cancer association is not confounded by other factors such

as diet, using aspirin or nonsteroidal antiinflammatory

drugs, smoking cigarettes, or body size. Other studies that

have evaluated confounding of the physical activity and

colon cancer association support our observation of lack of

confounding (1,7,9,16,20). Contradictory to our observa-tions

about confounding, we observe effect modification

between physical activity and several diet and lifestyle vari-ables

such as fiber and vegetable intake, energy intake,

BMI, and glycemic index. Previously, we reported that the

association between physical activity and colorectal cancer

was stronger among those without a family history of colo-rectal

cancer than among those with a family history of

colorectal cancer (20) and that energy balance, which in-cludes

the triad of BMI, energy intake, and energy expen-diture

importantly related to colon cancer risk (21). Differences

in associations across different strata of diet and lifestyle fac-tors

have implications for biological mechanisms as well as for

associations observed between studies of diet and colon cancer.

The observation that some exposures are more important

in reducing colon cancer risk among individuals with low

levels of physical activity hints at ways in which physical

activity may be operating: facilitating transit time of colonic

contents in the colon given the effect modification with

dietary fiber; influencing body weight given the modifying

effects with BMI; influencing insulin and IGF levels given

the effect modification with glycemic index and dietary

fiber; and perhaps influencing oxygen-free-radical forma-tion,

damage repair given the association with cigarette

smoking, lutein, and vegetables. Given our knowledge of

the physiological properties of physical activity and the

consistency of the association between physical activity and

colon cancer throughout the literature for both men and

women, it is highly likely that physical activity is involved

in a multitude of important biological mechanisms. Al-though

it is impossible to evaluate these mechanisms di-rectly

in large observational studies, evaluation of interac-tion

of physical activity with diet and lifestyle factors

provides useful clues for future mechanistic work in con-trolled

experimental setting.

An important conclusion from this analysis is that under-lying

population levels of physical activity can impair or

enhance the ability to identify colon cancer associations

with other risk factors. The level and variability of activity

in the population may determine whether factors such as

fiber, vegetables, or dietary patterns in general are seen as

importantly associated with colon cancer. Although the as-sociation

between physical activity and colon cancer does

not appear to vary by study design, other factors such as

dietary components show more variability in their associa-tion

with colon cancer between studies. It is possible that

some of these differences could stem from underlying dif-ferences

in activity levels of the populations studied. Many

population-based case-control studies have broad ranges of

exposure levels because they target total populations. These

studies often observe stronger associations for some dietary

factors such as vegetables and fiber. On the other hand,

cohort studies with more select populations may have higher

underlying levels of activity and less variability in the pop-ulation,

making it more difficult to detect some dietary

associations. In this study, factors such as calcium and folate

that are relatively consistent between case-control and co-hort

studies appear to be minimally influenced by level of

activity. Other dietary factors such as vegetables, fiber, and

energy appear to have stronger associations in those with

low levels of physical activity in this study.

In summary, high physical activity is consistently related

to lower risk of colon cancer. From the data presented here,

this association is not confounded by other colon cancer risk

factors. However, physical activity appears to have impor-tance

beyond its independent association with colon cancer.

The ability of physical activity to influence the relative

importance of other risk factors for colon cancer may be key

to understanding how physical activity lowers colon cancer

risk. It is likely that physical activity operates through mul-tiple

mechanisms that overlap with some of the other known

risk factors.

Cheers, Alan Pater