Extensive research has recently emerged indicating a clear association between diet and the risk of various types of cancers. Overall, results from studies have indicated that eating more fruits and vegetables and less processed foods and meats appears to decrease the risk of developing of cancer and/or improve outcomes of patients with cancer. In addition, levels of vitamin D, which can be synthesized from exposure to sunlight as well as dietary intake, are also being evaluated for a potential association with cancer. Specific food, outcome, and disease associations are still being researched to define which types of food can affect risks or prognoses of certain cancers.

Vitamin D

Vitamin D is a fat-soluble vitamin that comes from dietary supplements, foods such as fortified milk and cereal, certain kinds of fish (including salmon, mackerel, and tuna), and exposure to sunlight. Some theories suggest that vitamin D may play a role in the prevention of some types of cancer, including colon cancer.

To explore the relationship between plasma levels of vitamin D and risk of colorectal cancer, researchers evaluated information from the Health Professionals Follow-up Study.[1] This study began in 1986 and enrolled more than 51,000 male U.S. health professionals.

The current analysis focused on 179 study participants who had been diagnosed with colorectal cancer and a matched comparison group of 356 study participants who had not been diagnosed with colorectal cancer.

The plasma levels of vitamin D in the men with colorectal cancer were compared to vitamin D plasma levels in the men without colorectal cancer. An advantage of assessing plasma vitamin D (rather than dietary vitamin D) is that plasma vitamin D reflects both dietary sources of vitamin D as well as vitamin D from sun exposure.

The researchers then merged their results with results from the Nurses’ Health Study, another large study. Merging results from these two studies provided a larger number of subjects and also allowed the researchers to incorporate results from women (all of the Nurses’ Health Study participants are women).

• Increasing plasma levels of vitamin D were linked with a reduced risk of colon cancer in both the Health Professionals Follow-up Study and the Nurses’ Health Study.
• The relationship between plasma vitamin D and rectal cancer remains uncertain. Results from the Health Professionals Follow-up Study suggest an increase in risk of rectal cancer with increasing plasma vitamin D, while results from the Nurses’ Health Study suggest a decrease in risk of rectal cancer with increasing plasma vitamin D.

The results of this study provide additional evidence that vitamin D may be protective against colon cancer.

Meat and Other Foods May Raise Risk of Recurrence

An additional study further evaluating diet indicated that a diet high in meat, fat, refined grains, and sweets may increase the risk of cancer recurrence and death among patients with Stage III colon cancer.[2]

Although dietary factors such as high red meat consumption have been linked with the development of colorectal cancer, less is known about how diet influences survival following a colorectal cancer diagnosis.

To evaluate the effect of diet on colon cancer recurrence and survival, researchers conducted a study among 1,009 patients who had been treated with surgery and chemotherapy for Stage III colon cancer. Stage III colon cancer refers to cancer that invades one or more of the local lymph nodes but has not spread to distant organs.

The researchers evaluated dietary information provided by the study participants and identified two main dietary patterns: the “Western” diet, characterized by high intake of red and processed meats, refined grains, sweets, high-fat dairy products, and french fries; and the “prudent” diet, characterized by high intake of fruits, vegetables, whole grains, legumes, poultry, and fish.

• Individuals with the highest intake of the Western diet were more than three times more likely to experience a recurrence or death than individuals with the lowest intake.
• There was no link between level of intake of the prudent diet and risk of colon cancer recurrence or death.

This study suggests that diet may influence colon cancer outcomes. Individuals with higher intake of foods such as red meat, refined grains, and sweets had a higher risk of cancer recurrence and worse survival after Stage III colon cancer. Further research is needed to determine specific components of this dietary pattern that have the greatest impact on survival.

High Intake of the Nutrient Choline

Yet another study evaluating a potential association between dietary intake and colorectal cancer provided support that a high intake of choline—a nutrient found in foods such as red meat, eggs, poultry, and dairy products—may be linked with an increased risk of colorectal polyps.[3]

Some studies have suggested that folate, a water-soluble B-vitamin, may reduce the risk of colorectal adenomas. Choline is a nutrient that shares some biologic functions with folate, and researchers have hypothesized that choline may also reduce the risk of colorectal adenomas. Major food sources of choline include red meat, eggs, poultry, and dairy products.

To explore the relationship between dietary choline and risk of colorectal adenomas, researchers evaluated information from the Nurses’ Health Study.

The analysis focused on the 39,246 study participants who were initially free of cancer and polyps and who had at least one sigmoidoscopy or colonoscopy between 1984 and 2002. During follow-up, 2,408 of these women were diagnosed with a colorectal adenoma.

A self-administered dietary questionnaire was used to assess choline intake.

Compared to women with the lowest intake of choline, women with the highest intake were 45% more likely to develop a colorectal adenoma.

The finding that higher choline intake may increase the risk of colorectal polyps was unexpected. The researchers note that the apparent link between choline and colorectal polyps could be due to other components of choline-containing foods (rather than to choline per se), and should be investigated further.

The results from these three studies further support diet as a significant factor in the risk of developing colorectal cancer.  A diet high in fruits, vegetables, and whole grains not only appears to protect against cancers but also against non-cancerous diseases, and may improve overall health compared with diets high in meats, processed foods, and sweets.

References:

[1] Wu K, Feskanich D, Fuchs CS, Willett WC, Hollis BW, Giovannucci EL. A nested case-control study of plasma 25-hydroxyvitamin D concentrations and risk of colorectal cancer. Journal of the National Cancer Institute. 2007;99:1120-9.

[2] Meyerhardt JA, Niedzwiecki D, Hollis D et al. Association of dietary patterns with cancer recurrence and survival in patients with Stage III colon cancer. JAMA. 2007;298:754-764.

[3] Cho E, Willett WC, Colditz GA et al. Dietary choline and betaine and risk of distal colorectal adenoma in women. Journal of the National Cancer Institute. 2007;99:1224-31.

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