“Aspartame Causes Cancer!”: A Research Scientist Breaks it Down

Yesterday, the World Health Organization (WHO) released findings that aspartame, the widely used artificial sweetener that’s found in diet cokes and water enhancers, has a “possible link” to cancer in humans.

Today, “aspartame causes cancer” is one of the top trending searches on Google.

As a research scientist, I get really frustrated when findings like this get sensationalized. So, I’d like to break these findings down from an empirical perspective. If you’ve been here awhile and are wondering why I’m referring to myself as a research scientist instead of a cognitive psychologist, allow me to explain (I promise it’s relevant). Cognitive psychologists are not therapists. We are generally research psychologists. We study psychological phenomena in laboratory or experimental settings, collect and analyze the data with rigorous statistical techniques, and publish our findings in scholarly journals. We are well versed in the empirical process — in fact, our training is just as much on proper research methods and statistics as it is on psychology. I taught upper division Research Methods and Statistics at the University of Memphis, and know a thing or two about the empirical process and how to interpret findings.

So, let me talk about how findings like the ones published by the WHO yesterday get sensationalized, distorted, and misunderstood.

My main point here: you don’t have to be terrified of aspartame. But it is a good idea to correctly understand the available information and make an informed decision.

The WHO has reported that aspartame is “possibly carcinogenic to humans.” That sounds scary. And listen, before I go any further, let me just say that it is perfectly valid to want to stay away from anything and everything that has been even tangentially linked to cancer. Having lost family members to cancer myself, I understand why a person would decide not to risk it at all. But for those of us who consume aspartame occasionally and want to know exactly how big a threat it is to us before we make a decision, I think this is an important conversation to have.

Here are a few things to consider about the “possibly carcinogenic to humans” label that has been given to aspartame:

#1. Many things we consume every day have been given the same label, and we don’t even know it.

Because these items haven’t been sensationalized like aspartame has, they have completely flown under the radar for most of us. Did you know that things like fried potatoes, some baked goods, and even coffee form a chemical called acrylamide that has been designated as a possible carcinogen since 1994? In 2004, the IARC labeled formaldehyde as a possible carcinogen, which is found in many of the cosmetics you can buy at the drug store. In fact, formaldehyde has been labeled as a Group 1 carcinogen — meaning that there is sufficient scientific evidence to support its link to cancer. As I’ll get into in a moment, there is far more evidence for the link of formaldehyde to cancer than of aspartame. But because aspartame gets such an obscene amount of attention from the media, we fear it more than we fear the cosmetics we apply to our faces every day. Which leads me to my next point:

#2. Many media outlets latch on to phrases they see in scientific publications and really distort the meaning of those phrases.

The phrase “possibly linked to cancer in humans” doesn’t tell me much as a scientist. My natural first questions are, how strong is that link? Is the connection statistically significant? How was the testing done — was it done on humans, or on animals? Were other variables accounted for, like weight, age, amount of consumption, pre-existing conditions?

When news and online media give their two-sentence sound bite or headline proclaiming the possible link between aspartame and cancer, they really don’t give us enough information with which to evaluate the claim. To use a really over-simplified example, there is also a possible link between flying in an airplane and dying in a plane crash. We all know this link. We all understand this risk. But because the possible link is so profoundly small, most of us are willing to take the risk. Because the news doesn’t sensationalize this risk, doesn’t yell about the “possible link between airplane travel and death by plummeting to the ground,” we don’t make much fuss over it. Unfortunately, the media just really can’t be trusted (in my opinion) to convey scientific information to us in a reliable way. Which, of course, brings me to my third and most important point:

First, the majority of studies on the relationship between aspartame and cancer have been done in lab rats. I’m not going to get into the moral or ethical dilemma of animal testing in this article; I’ll save that for another time. For now, it’s just important to recognize that animals will always have different responses to chemicals than we do because their genetic make-up is different. Does that make the findings totally un-useful? Of course not. It just means we need to take those findings with a grain of salt. For one thing, although the link between aspartame and cancer has been found in rats, studies conducted on other animals have not. For another, the strength of the link between aspartame and cancer in rats is very small, and is still bigger than the strength of the link between aspartame and cancer in humans.

Second, because of the ethical concerns of doing real, empirical studies on the link between aspartame and cancer in humans, all we have to rely on is observational data. Empirical studies involve a control group and an experimental group. To do an empirical study of the impact of aspartame on humans, the experimental group would need to be administered high volumes of aspartame, and the control group would receive a placebo. Then, the incidence of cancer between the two groups would be analyzed. Obviously, this is unethical and inhumane. So, the only way to study the link between aspartame and cancer is to either: (a) find people who have already been diagnosed with cancer and then give them retroactive surveys about their intake of aspartame throughout their lifetime, or (b) find two groups of people — one that consumes aspartame and one that doesn’t, and follow them longitudinally (over a very long time) to measure the incidence of cancer between the two groups. As you can see, and as the scientific community has pointed out, this isn’t a very scientifically controlled way of studying aspartame and cancer.

Third, the best available findings we have estimate that a 180 pound (ca. 82 kg) person would need to drink 40 cans of diet soda a day, over many years, to be at risk of getting cancer from aspartame. See the problem? It’s the same issue as the airplane scenario above. Yes, there is a link between aspartame and cancer. If that’s the only information we have, it seems reasonable to stop consuming it. But when we understand that we would have to consume an almost impossible quantity of it to get the carcinogenic effect, it changes how we think about it. And these are things that don’t get reported in the sensationalized media.

Lastly, the findings from human studies on the link between aspartame and cancer have been inconsistent, limited in design and scope, and not well controlled. Controlled means that you have accounted for other variables that might have an influence on your findings. To give just one small example, it’s plausible that a high proportion of people who consume aspartame do so because they want to lose weight. Since obesity is also linked to cancer and many other physical ailments, there may be other variables that produce cancer in people who consume aspartame, but those variables aren’t being studied or accounted for. This makes it nearly impossible to accurately and reliably interpret the findings.

So, is it time to give up aspartame?

Ultimately, that’s a personal question. You have to make decisions based on what you are most comfortable with, and it is perfectly reasonable to stay away from anything that has even the slightest link to cancer. And, if we’re being honest, it’s probably better to stick to water and other beverages that don’t contain aspartame. That said, if you’re consuming aspartame minimally, as a small part of your daily diet, there isn’t much need to worry. Most things are perfectly fine in moderation, and the scientific community seems to indicate that aspartame is one of those things.

On a personal note, as a migraine sufferer, I am far more concerned about the link between aspartame and migraines. That relationship has been far better studied, with much more conclusive evidence. Just something to consider.


Amber Wardell is a doctor of psychology and author who speaks on women’s issues related to marriage, motherhood, and mental health. Subscribe to the free newsletter to get exclusive content delivered to your inbox and to never miss an upload.

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