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Providing perspectives on recent research into vitamins and nutritionals


Study of Dietary Changes After Cancer Diagnosis Highlights Pitfall of Epidemiological Research

By Julia Bird

Most of us, at one time or other, have made a behavior change to improve our health. Rather than being a gradual process, decisions to stop smoking, get more active, or eat a healthier diet tend to be made after a trigger or cue sets us on the path to better lifestyle choices. Cues may come from seeing a certain news report, or noticing information provided by a public health campaign. Advice from a doctor regarding disease prevention can be an effective trigger. Behavior change may be “infectious”: if a friend or relative has recently stopped smoking, it may provide a stimulus to stop. I know for myself, a relationship break-up over a decade ago from a boyfriend who told me that I looked stupid when I was jogging was the trigger I needed to get off the sofa and exercise more often. A disease diagnosis, for one’s self, a relative, or even in a famous person, may also be a cue to change behavior or undergo a screening test for a particular disease.

But herein lies one of the problems with research into behavior change, as exemplified by Bours and associates: a diagnosis of a certain disease is likely to result in a behavior change towards a “healthier” lifestyle. They used data from the PROFILES registry  in the Netherlands, which is designed to facilitate the study of the health of patients with a cancer diagnosis. 1458 colorectal cancer survivors were asked about dietary changes they made after their cancer diagnosis, including changes in 11 food components, and the use of dietary supplements. Motivations for behavior change were also included in the survey, and could include changes to support recovery or to prevent disease recurrence.

Over half of the cancer survivors made a positive change to their diet or started to take dietary supplements after their diagnosis. The authors found that around one third of the cancer survivors made a change in their diet since the diagnosis, and a further third started to use dietary supplements. 15% both changed their diet and started to use supplements. These changes occurred despite only 17% receiving advice from a health care provider to change their diet. On average, people who changed their diet changed their intake of on average 7 food components, including increasing intake of fruit and vegetables, whole grain, and reducing salt and meat consumption. For supplement users, there were some changes in type of supplement used before and after the diagnosis in addition to more survivors using supplements. In particular, more people started to use vitamin D, magnesium, fish oil, multivitamins, and other supplements.  

People who made dietary changes did so to prevent cancer recurrence (44%), and less often to support recovery (20%) or reduce cancer-related complaints (19%). For dietary supplement users, 33% took them to support therapy and recovery, 25% to prevent cancer recurrence, and rarely (4%) to reduce cancer-related complaints. Dietary supplement users with another reason reported most commonly that their primary motivation was to improve general health and prevent disease.

This study agrees with data from the US, that shows that dietary supplement users use supplements to “maintain” or “improve” their health (Bailey et al.). Even so, it is clear that a cancer diagnosis was a major trigger for people to make a change in their diet or to take up the use of dietary supplements. And this is a big issue with epidemiological research. Findings that the use of dietary supplements have been associated with a greater risk of cancer, that have been promoted widely in the media, is not likely to be a causative association. Rather, it seems that a change to start using dietary supplements is a result of a cancer diagnosis. It is also possible that people who start to notice changes in their health due to undiagnosed cancer may turn to supplements as a way to improve their well-being. Be wary when the next media bomb linking supplement use and disease hits our airwaves, newspapers, Twitter feeds and RSS readers. The best type of study – a large, randomized trial of multivitamins conducted over a long period of time in a healthy population, the Physicians Health Study II – showed a modest benefit in regards to cancer reduction. Dive into the original research report and check that multivitamin use could be a result of cancer diagnosis and not a cause.


Main citation:

Martijn J. Bours, Sandra Beijer, Renate M. Winkels, Fränzel J. van Duijnhoven, Floortje Mols, José J. Breedveld-Peters, Ellen Kampman, Matty P. Weijenberg and Lonneke V. van de Poll-Franse. Dietary changes and dietary supplement use, and underlying motives for these habits reported by colorectal cancer survivors of the Patient Reported Outcomes Following Initial Treatment and Long-Term Evaluation of Survivorship (PROFILES) registry. British Journal of Nutrition, available on CJO2015. doi:10.1017/S0007114515001798.


Supporting citations:

Bailey RL, Gahche JJ, Miller PE, Thomas PR, Dwyer JT. Why US adults use dietary supplements. JAMA Intern Med. 2013 Mar 11;173(5):355-61. doi: 10.1001/jamainternmed.2013.2299.

Gaziano J, Sesso HD, Christen WG, et al. Multivitamins in the Prevention of Cancer in Men: The Physicians' Health Study II Randomized Controlled Trial. JAMA. 2012;308(18):1871-1880. doi:10.1001/jama.2012.14641.