Within the last week, an article was published on diet soda and cners which received a lot of attention. The attention was for being inaccurate or misleading. Several peer reviewed journals had rejected the article before it was finally accepted by the American Journal of Clinical Nutrition. The issue was over whether or not the conclusion of the authors, that there was an association between diet soda consumption and certain cancers, was supported by the evidence. The main outcomes of interest were non-hodgkins lymphoma and multiple myeloma. The researchers found a slightly elevated risk for NHL in men only. This was not an experiment so there is no statement of cause. NO one - not even the scientists who did the research - is saying that diet soda causes anything.
One of the issues that author's of this study brought up was the rare occurrence of the cancers in any of the people in the study. I read the article and found some problems as well. My point of writing the post tonight was to let you know two things - but as I read the article a second time, something else stood out to me which I will share at the end.
First - I agree - this study is weak. As I was reading I thought this study felt familiar and that is because this spring the same authors published research on soda consumption and heart disease. In fact, I blogged about it ~ here. They are using the same data to answer several research questions. That is okay, but its where the data is coming from that caught my attention. In this study, the authors point out that the majority of survey respondents (they collected the info through mail surveys every two years starting in 1976 and 1986) did not drink a lot of soda. WHAT?! Who doesn't drink soda in America?! This made me go back to the page that described the research. The information used in this study came from two groups of people enrolled in different studies. One group was women who were nurses. They started the study in 1976 when they were between the ages of 30 and 55. The second group was male health care professionals (doctors, etc). They completed their first survey in 1986 when they were between the ages of 40 and 75.
Every two years from the start, both groups were re interviewed, or completed follow up surveys. Every other time, or every four years, they completed a food frequency questionnaire. For the FFQ, they were asked to report on the frequency of consumption of around 130 items, including soda. The last survey took place in 2006. The people were between age 60 and 95 at the last time point. Some had died and some had been diagnosed with cancer. Those cases were counted and then the researchers looked to see if there was any association between the amount of soda, diet or regular, consumed and the rate of cancer in the groups. As I said, a small increased risk was found in the men, but it was also found for regular soda. The risk for these particular cancers was rare overall.
Here are three very important things to consider about the people who were in this study. They were all born between 1911 and 1946 (so yes, now I can see why they were not soda drinkers)(I failed to make this point in the blog post last March). They were all in health care professions. They were mostly white people.
Here is something very important to consider about their food and soda intake. They were asked to report the frequency of food and beverage consumption over the past YEAR. Can you remember what you had last week?
Therefore, the people for whom these results were calculated do not represent average Americans. The information they provided on their own behavior was probably inaccurate due to recall bias (forgetting or not wanting to tell the truth are two type of bias - or errors).
Does this study suggest that there is a link between diet soda and cancer - specifically aspartame sweetened diet soda - NO.
Is there something more to say about aspartame? YES.
I will share that in my next post. Here's a teaser... maybe its the diet soda Mayor Bloomberg should limit. This comes from the girl who has about 9 diet sodas a week.
study citation: Schernhammer, E. S., Bertrand, K. A., Birmann, B. M., Sampson, L., Willett, W. W., & Feskanich, D. (2012). Consumption of artificial sweetener– and sugar-containing soda and risk of lymphoma and leukemia in men and women. The American Journal of Clinical Nutrition.