Nutritional risks and colorectal cancer in a portuguese population

P. Ravasco*, I. Monteiro-Grillo*^,**, P. Marqués Vidal* y M.ª E. Camilo*

*Unit of Nutrition and Metabolism, Institute of Molecular Medicine of the Faculty of Medicine of the University of Lisbon, Avenida Prof. Egas Moniz 1649-028 Lisboa, Portugal. p.ravasco@fm.ul.pt **Radiotherapy Department of the Santa Maria University Hospital, Avenida Prof. Egas Moniz 1649-035 Lisboa, Portugal and Unit of Nutrition and Metabolism, Institute of Molecular Medicine of the Faculty of Medicine of the University of Lisbon, Avenida Prof. Egas Moniz 1649-028 Lisboa, Portugal. imonteiro.grillo@hsm.min-saude.pt

Correspondence: Paula Ravasco
Unidade de Nutrição e Metabolismo
Instituto de Medicina Molecular
Faculdade de Medicina de Lisboa
Avda. Prof. Egas Moniz
1649-028 Lisboa (Portugal)
E-mail: p.ravasco@fm.ul.pt

Recibido: 21-IX-2004. ]]> Aceptado: 15-XI-2004.

Introduction

Dietary epidemiology worldwide ascribes the incidence of about a third of cancers to nutritional factors^1,2; their identification in different geographical areas is a priority since about 50% of cancers are estimated to be preventable by adequate nutrition and body weight, regular physical activity and tobacco abstention^1,3. Notwithstanding individual genetics, nutrient-gene interactions and nutrient-modulated gene expression may further explain cancer incidence and progression^4-7.

For colorectal cancer (CRC) some nutritional components are putatively accepted as risk factors, e.g. refined carbohydrates⁸ and lipids⁹, whereas protein and alcohol are still controversial^10-14; conversely, other nutrients are regarded as protectors, e.g. insoluble fiber^15,16 and micronutrients^17-19.

The increasing incidence of colorectal cancer (CRC) in Portugal calls for objective dietary epidemiological data. Thus, our main purpose was to address this issue and investigate potential indicative patterns with both clinical and Public Health relevance. This study aimed to characterize and identify the prevalence of high-risk life-styles and diet patterns, based on detailed food composition analysis in all classical and recently identified bioactive food constituents, and their associations with colorectal cancer.

Materials and methods

This cross-sectional study approved by the University Hospital Ethics Committee was conducted in accordance with the Helsinki Declaration of 1975 as revised in 1983, and designed to characterize and identify the prevalence of high-risk life-styles and diet patterns and their associations with colorectal cancer. All participants gave their informed consent and individual data were registered in forms preconceived for statistical analysis.

Subjects

Between July 2000 and January 2002, all consecutive ambulatory patients with CRC referred to the Radiotherapy Department (n = 70) were considered eligible. For every patient the clinical and CRC family history, and co-morbidities were registered. Diagnosis was established by histology and imaging methods, according to the TNM classification (American Joint Committee on Cancer)²⁰. The control population was recruited at community health centers or amongst administrative/technical hospital staff, and consisted of 70 randomly selected subjects without any cancer history, matched for sex and age, the latter stratified in 5-year intervals; only subjects with no reported recent weight changes or dietary restrictions were included.

 Height was obtained with a stadiometer and weight was determined with a calibrated floor Jofre^® scale. Body mass index (BMI) was calculated and categorized as severe malnutrition (≥ 16 kg/m²), malnutrition (> 16-19 kg/m²), adequate (≥ 20-25 kg/m²), overweight (> 25-30 kg/m²), stage 1 obesity (> 30-35 kg/m²), stage 2 obesity (> 35-40 kg/m²) and stage 3 obesity (> 40 kg/m²)²¹. Jackson's questionnaire categorized physical activity level in a 0 to 7 scale, ranging from "did not perform any regular intense physical exercise or leisure activity" to "did perform regular intense physical exercise"²². According to the previous and present smoking habits, subjects were defined as non-smokers (never or occasional consumption) or smokers (regular consumption >10 years even if not currently consuming); number of packages per day, duration of consumption (years) and the total number of packages per year was calculated.

Dietary pattern

The diet history method (including alcohol consumption) comprising a 24-hour recall food questionnaire, a food frequency questionnaire and a 72-hours diet diary (2 week days and 1 weekend day)^23,24 was always used; the same registered research dietician (PR) interviewed all subjects who were also questioned on the use of dietary supplements. The software DIETPLAN version 5 for Windows (Forestfield software Ltd 2002, Horsham, UK) was used to analyze nutrient contents of foodstuffs and meals. In what concerns alcohol consumption, the duration (years), type of alcoholic beverages and intake frequency were registered, the usual intake amounts were quantified by using photographic models²⁵, and the total alcohol intake was calculated (expressed in grams per day). Total nutrient and alcohol intake were compared with the Dietary Recommended Intake (DRI)^26,27; for flavonoids or isoflavones, lacking established DRI, comparisons were based on median intakes and the average content of rich dietary sources. Nutritional intake analysis comprised the foods/nutrients classically associated with CRC and "new" components, whose relevance has been recently suggested in vitro.

Statistical Analysis

Statistical analysis was conducted using SPSS 10.0 (SPSS Inc, Chicago, USA) and EPI-Info 2000 (CDC, Atlanta, USA). Parametrical (Students't) and non-parametrical (Wilcoxon) tests determined differences in nutritional status and life-style variables between cases and controls. Correlations were assessed by Spearman rank method. For both food and total nutrient intake, subjects were categorized according to quartiles of intake. We used relative risk as a measure of association, defined as the incidence of CRC in each food intake quartile, divided by the corresponding rate among the subjects on the lowest quartile. Age-adjusted relative risks were calculated after stratification according to 5-year categories. Proportional hazards models were used to adjust for multiple risk factors simultaneously (age, BMI, CRC family history, tobacco, physical activity, co-morbidities). In addition stratified analyses were conducted to determine whether the influence of nutritional intake was modified by other risk factors for CRC. All P values are two-sided. To evaluate the influence of measurement error on our findings, we used a correction procedure that adjusts the relative risks and confidence intervals to account for errors in assessing nutritional intake²⁸. For all statistics, significance was accepted at the 5% probability level.

Results

Characteristics of the study population are shown in table I; subjects with type II diabetes mellitus and/or hypertension were just treated with drug therapy and did not follow any specific diet. There was an overall trend associating a lower BMI to higher level of physical activity (p = 0.09) though the latter was unrelated to CRC risk. In what concerns smoking there were 29 current smokers amongst CRC patients and 8 amongst controls, all female patients and controls were non-smokers; there was a smoking-associated relative risk of 1.90 (1.86-1.97). None of the participants was taking nutritional supplements.

]]> Age-adjusted and multivariate analyses showed that both the diet pattern and the intake of specific nutrients were strongly associated with the incidence of CRC, in the highest as compared with the lowest quartile, tables II, III and IV. In multivariate analyses, each increment of 4 servings per week of red meat, smoked salted pork products and 100g of alcohol corresponded to an increased relative risk of 1.29 (95% CI: 1.21-1.34). In what concerns nutrients, each increment of at least 50% in the weekly intake of protein, total fat, saturated fat, cholesterol, refined carbohydrates, iron, vitamin B₁₂,sodium and alcohol corresponded to an increased relative risk of 1.53 (95% CI: 1.47-1.59). Conversely, the increment of 4 servings per day of green leafy vegetables, fruits and fish corresponded to a decreased relative risk of 0.35 (95% CI: 0.29-0.41). Each increment of at least 50% in the weekly intake of n-3 fatty acids, insoluble fibber, vitamin E, flavonoids, isoflavones, ß-carotene, folate and selenium corresponded to a decreased relative risk of 0.31 (95% CI: 0.26-0.37). Further nutrient analysis in patients identified several differences between current intake and the DRI, tables V and  VI. The median intake of flavonoids and isoflavones was also significantly lower (p = 0.001) than the comparison value.

Nutrition is a putative though controversial risk factor for CRC. This prospective study thoroughly investigated epidemiological data previously unknown in Portugal. The diet of "healthy subjects" was indeed similar to the Mediterranean pattern^{1,29, 30}, unlike CRC patients' monotonous and unbalanced diet, characterized by high risk nutritional deficits and surpluses. Patients' diet was characterized by frequent and excessive consumption of red meat and processed meat products resulting in excessive intake of animal protein, saturated fat, cholesterol, vitamin B₁₂ and haem iron; likewise, refined carbohydrates and alcohol consumption was overabundant. Conversely, the intake of fruits and vegetables was lower than the recommended 5-9 daily portions³¹ with subsequent deficits of insoluble fiber, vitamins, minerals and other protective compounds, e.g. flavonoids^29,32 and isoflavones³³; the intake of fish and n-3 fatty acids was also very low. This diet pattern was associated with smoking habits in 45% of patients and with low physical activity in 77%, though the latter was unrelated to CRC risk unlike previously suggested^34,35. Among life-style risk factors, several case-control studies demonstrated a consistent association between tobacco consumption and CRC^35-37; our results are only concordant in men since women were non-smokers. CRC risk associated with alcohol abuse is controversial^{14,38, 39}, potentially enhanced by concurrent vita-min deficits; in this study women were teetotal, thus alcohol was a risk factor just for men whose diets were also markedly deficient in various vitamins, similarly to what we have previously shown^40,41.

Epidemiological data concerning energy intake and CRC have been inconsistent, excessive energy intake and increased risk⁴² versus no risk⁴³. In our study, high energy intake represented an 85% increase of CRC risk, and energy sources, e.g. total fat and refined carbohydrates, which independently represented 187% and 79% increased risk, respectively; this association is consistent with their pro-carcinogenic effect on colorectal cell lines^9,44. The association between excessive protein intake and CRC has been inconsistent, no risk^11,12 versus increased risk¹⁰, the latter was corroborated by our study; the citotoxicity of protein metabolism end products may act as a carcinogenesis promoter⁴⁵.

A marked reduction of CRC risk associated with frequent fish consumption and n-3 fatty acids was a major novelty of this study; its relevance may bear to their anti-inflammatory effects⁴⁶ and potential pro-apoptotic properties⁴⁷.

A high intake of insoluble fiber is consistently recommended given its ascribed direct^48-50 and indirect protective roles^8,51. CRC patients' diet was markedly deficient in insoluble fiber that whenever consumed according to recommendations³¹ is expected to result in an 85% risk reduction.

Deficits of antioxidants are likely to promote oxidative stress and carcinogenesis⁵². Patients' diet contained a marked surplus of haem iron associated with free radicals production⁵³, while the concurrent vitamin E deficit forbear their protective effects^54-56. Epidemiology also reports an association between low blood α-tocopherol concentrations and increased CRC risk⁵⁷, our study is however the first to show that an adequate intake of vitamin E is associated with 75% reduced risk. Selenium, seldom evaluated⁵⁸, now revealed a protective effect. Flavonoids are a hot research topic due to their antioxidant⁵⁹, pro-apoptotic properties⁶⁰, and cell proliferation inhibitory effect⁶¹; this study first shows epidemiological data on their protective effect with 75% risk reduction. Fruits and vegetables, main sources of vitamin C and ß-carotene, are rich in numerous beneficial compounds^62-64; indeed a significant protective effect higher than 60% was attributed to an adequate intake of green leafy vegetables, fruits and legumes.

In spite of the potential physiological properties of isoflavones^33,65, exclusively conveyed by vegetables, our study is so far the first to have identified a significant protective effect against CRC.

Epidemiological evidence associates folate deficiencies to CRC incidence, since chronically deficient diets determine DNA hypomethylation and chromosomic alterations (66, 67). Two studies showed a modest risk increase associated with prolonged deficits of vitamin B6, methionine, folate and vitamin B12^68,69. Notwithstanding the lack of data related to excessive intake, vitamin B12 in excess may compete with folate on the remethylation cycle and determine DNA hypomethylation¹⁹. In CRC patients' diet, vitamin B6 and folate was >3 times below the DRI whereas vitamin B12 in-take was 3 times higher the DRI; both deficit and surplus were associated with >70% increased risk.

Despite the study's limitations related to its sample size, data were adjusted for all recognized confounding variables and still pinpointed nutrients identified worldwide since 1982 as risk factors for CRC²⁷ and reinforced the protective of others, whilst disclosing emerging protective nutrients^33,59_, ⁶⁰. Given the worldwide high and increasing incidence of CRC, investigations of nutrient-carcinogenesis interactions are warranted to further stress the relevance of preventive nutrition.

We are indebted to the medical, nursing and technical staff of the Radiotherapy Department of the Hospital of Santa Maria.

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