What is the Relationship Between Aspartame and Cancer?

Despite long-standing rumors, there is currently no provable link between the artificial sweetener aspartame and cancer. Findings from a variety of global studies demonstrating this are backed up by the United States Food and Drug Administration (FDA), the National Cancer Institute (NCI), the American Cancer Society® (ACS), and the European Food Safety Authority (EFSA), among others. It seems that most fears about aspartame originate from a misunderstanding of what happens to it in the body, several studies that appeared to link it to health problems, and a widely forwarded e-mail claiming that it causes a wide range of illnesses. Despite studies suggesting that it is safe, some people do choose to avoid consuming it because of individual sensitivities or just to be on the safe side.

One of the most common claims about aspartame is that it breaks down into carcinogens, substances that increase a person's risk for cancer. This generally comes from a misunderstanding of how it's metabolized. Once in the body, aspartame is broken down into aspartic acid, phenylalanine, and methanol. Those who claim that there's a link between aspartame and cancer point to how the body converts methanol into formaldehyde and formic acid, both of which are carcinogens.

This is how the process happens; however, tests on people's blood after they consume aspartame show that the concentration of aspartic acid and methanol is extremely slight, and in many cases doesn't even show up. Phenylalanine does show up on tests, but usually only if a person consumes a lot of aspartame — the equivalent of a 155 lb (70 kg) person drinking more than 17 oz (355 ml) diet sodas. Additionally, aspartame is not a major source of aspartic acid, phenylalanine, or methanol. For instance, a glass of fruit juice has more methanol than a can of diet soda, and an egg has three times the phenylalanine.

Other arguments about aspartame and cancer often stem from a few studies: one by Olney et al. in 1996; one by Trocho et al. in 1998; and one by Soffritti et al. in 2007. The Olney study looked at data about the number of people who developed brain tumors in the US from 1975 to 1992. It concluded that there was a link between aspartame and brain cancer because there was a significant increase in reported brain tumors in the mid-1980s, which was when aspartame came on the US market. The study was criticized for misinterpreting the data: brain tumor diagnoses actually started increasing in the early 1970s and leveled out in the mid-1980s. Reviewers also criticized it for failing to consider other possible causes of the increase in reports, like improvements in diagnostic methods.

The Trocho study attempted to show a link between aspartame and liver cancer, suggesting that it caused certain potentially toxic or carcinogenic radioactive DNA and protein substances to build up in the livers of rats. The findings and methodology of this study were criticized as well. The way the authors tracked the broken down components of aspartame in the test rats was by making the methanol part radioactive so it could be traced. Since methanol breaks off when it's metabolized and moves throughout the body, and the authors didn't identify the substances in the liver as coming from their methanol, it can't be proven that they were caused by aspartame. Similar studies haven't produced the same results.

The more recent Soffritti study suggested that aspartame caused breast cancer, lymphomas, and leukemia in test rats. Researchers criticized the way the study was carried out and the way the data was interpreted. One of the main criticisms was that the authors failed to consider that the type of rats they were using are particularly prone to certain cancers. Another was that the study only considered specific types of tumors, and did not consider other possible reasons that the rats might have developed cancer. Other studies in which rats were given much higher dosages did not yield similar results.

People have also claimed that aspartame causes a wide range of birth defects, Attention Deficit Disorder (ADD) and Attention Deficit Hyperactivity Disorder (ADHD), Alzheimer's and Parkinson's diseases, multiple sclerosis, lupus, diabetes, and seizures. Some also say it damages brain cells and causes mood disorders. Despite these claims, tests have been done on its effects in a wide variety of groups, including adult men and women, children and teens, diabetics, phenylketonurics, those with mood disorders, people with Parkinson's disease, epileptics, and those with ADD and ADHD, among others. No link could be established between any of those conditions and aspartame, even when the people in the studies were given much more than a normal person consumes.

Some people do have individual sensitivities to aspartame, which can cause a range of symptoms, including headaches and mood changes. Also, those with phenylketonuria (PKU) should avoid consuming it, since their bodies cannot metabolize phenylalanine properly. This can lead to a buildup of phenylalanine in the body, which can damage the nervous system and brain. Some people who don't have sensitivities or PKU choose to avoid it as well, since research on the relationship between aspartame and cancer is ongoing, and findings could change.