**5. Physical activity**

Physical activity (PA) includes all movements performed in daily life, including sport, whether recreational or competitive [30], as well as that performed in occupational, transport, recreational, and household settings [7]. In epidemiological studies, PA is computed by combining intensity, duration, and frequency of different types of PA, with subjects being classified into three levels of PA, namely, low, moderate, or high. PA is usually divided into four types of activity related to occupational, transport, recreational, and household settings. Total PA is calculated as the sum of the four types or any of the four types that are presented as all-type PA. Thus a major barrier to conducting meta-analyses is the disparity between the measures of PA [7].

**17**

*6.1.1 Mechanism*

*Effectivity and Modulating Pathways for the Prevention of Colorectal Cancer: Diet, Body Fatness…*

There is convincing evidence that all types of PA, when comparing the highest and lowest levels, are protective against colon cancer with a significant inverse association being observed for total PA and CRC. However, no significant associations were observed for rectal cancer and either total or recreational PA when comparing the highest and lowest levels. For recreational PA and colon cancer risk, three published meta-analysis reported inverse associations. In addition, there is robust evidence for mechanisms operating in humans. However, dose-response relationships could not be determined [7, 8]. The protective effect was similar for proximal and distal colon cancer and was stronger for men than women [7]. More physically active subjects had a 24% decreased risk of CRC compared to those who lead a more sedentary lifestyle [55]. It has been reported that those who exercise regularly decrease their CRC risk by 40%, regardless of BMI [56]. In addition, 30 min of daily

PA reduces body fatness and therefore has a beneficial effect on CRC risk, possibly due to a reduction in insulin resistance and inflammation [50, 53, 54]. However, it is unclear whether PA that is not accompanied by weight loss has a significant impact on these pathways. Other mechanisms through which PA may lower CRC risk include the stimulation of digestion and reduction of gastrointestinal (GI) transit time, although robust data to support this mechanism in humans is limited [58]. Overall, mechanistic

The Women's Health Initiative failed to show a significant relationship between calcium supplementation and the risk of developing CRC among postmenopausal women [59], while a meta-analysis of cohort studies reported a significant inverse relationship for colon and CRC when comparing the highest to lowest levels of calcium supplementation [60]. As there is evidence of plausible mechanisms in humans, the Continuous Update Project (CUP) panel concluded that taking calcium supplements probably protect against CRC, based on evidence derived from a dosage of more than 200 mg per day [8]. The evidence was generally consistent and showed inverse associations across a range of intakes (200–1000 mg). RCTs reported a nonsignificant inverse association for calcium and vitamin D supplementation compared to placebo, after excluding women using calcium or vitamin D supplements at baseline. Although no dose-response meta-analysis could be conducted, six of the eight cohort studies reported inverse associations [8]. Predominant evidence indicates an increased CRC risk among individuals with a calcium intake lower than 700–1000 mg/day. It would therefore be reasonable to encourage individuals to increase their calcium intake to a level above this range,

data to support a link between PA and CRC are moderate in strength [8].

**6.1 Calcium changes made to this section are indicated in blue**

while recognizing that available data yielded inconsistent results [4].

A proposed mechanism for the protective properties of calcium against CRC is its ability to bind to unconjugated bile acids and free fatty acids (FFAs), thereby limiting their toxic effects on the colorectum [4, 61]. Cell culture studies suggest that it may also suppress cell proliferation and promote cell differentiation and

*DOI: http://dx.doi.org/10.5772/intechopen.84764*

**5.1 Mechanism**

**6. Supplementation**

moderate exercise result in an 11% reduction in CRC [57].

*Effectivity and Modulating Pathways for the Prevention of Colorectal Cancer: Diet, Body Fatness… DOI: http://dx.doi.org/10.5772/intechopen.84764*

There is convincing evidence that all types of PA, when comparing the highest and lowest levels, are protective against colon cancer with a significant inverse association being observed for total PA and CRC. However, no significant associations were observed for rectal cancer and either total or recreational PA when comparing the highest and lowest levels. For recreational PA and colon cancer risk, three published meta-analysis reported inverse associations. In addition, there is robust evidence for mechanisms operating in humans. However, dose-response relationships could not be determined [7, 8]. The protective effect was similar for proximal and distal colon cancer and was stronger for men than women [7]. More physically active subjects had a 24% decreased risk of CRC compared to those who lead a more sedentary lifestyle [55]. It has been reported that those who exercise regularly decrease their CRC risk by 40%, regardless of BMI [56]. In addition, 30 min of daily moderate exercise result in an 11% reduction in CRC [57].
