What is aspartame?
Aspartame is one of the most common artificial sweeteners in use today. It is sold under the brand names NutraSweet® and Equal®. Aspartame is made by joining together the amino acids aspartic acid and phenylalanine. Amino acids are the building blocks of proteins and are found naturally in many foods.
Aspartame is used in many foods and beverages because it is about 200 times sweeter than sugar, so much less of it can be used to give the same level of sweetness. This, in turn, lowers the calories in the food or beverage.
Rumors claiming that aspartame causes a number of health problems, including cancer, have been around for many years. Many of these continue to circulate on the Internet.
How are people exposed to aspartame?
Aspartame has been used in the United States since the early 1980s. It is now found in thousands of different food products. Aspartame is commonly used as a tabletop sweetener, as a sweetener in prepared foods and beverages, and in recipes that do not require too much heating (since heat breaks down aspartame). It can also be found as a flavoring in some medicines.
In the body, aspartame is broken down into phenylalanine, aspartic acid, and methanol. Methanol can be toxic in high amounts, but the amounts that result from the breakdown of aspartame is lower than with many “natural” foods. For example, drinking a liter of diet soda would lead to consumption of 55 milligrams (mg) of methanol, as compared to as much as 680 mg of methanol from a liter of fruit juice.
Phenylalanine and aspartic acid are amino acids and are naturally present in many foods that contain protein. They do not cause health problems in most people. However people with the disease phenylketonuria (discussed in more detail later on) need to restrict their intake of phenylalanine, and so are usually counseled to avoid aspartame.
How is aspartame regulated?
In the United States, artificial sweeteners such as aspartame are regulated by the Food and Drug Administration (FDA). These products must be tested for safety and approved by the FDA before they can be used. The FDA also sets an acceptable daily intake (ADI) for each sweetener, which is the maximum amount considered safe to consume each day during a person's lifetime. The ADI is set to be about 100 times less than the smallest amount that might cause health concerns, based on studies done in lab animals.
The FDA has set the ADI for aspartame at 50 milligrams per kilogram (mg/kg) of body weight. The European Food Safety Authority (EFSA), which regulates food additives in the European Union, recommends a slightly lower ADI for aspartame, at 40 mg/kg.
To put the ADI for aspartame in perspective, this would be 3,750 milligrams per day for a typical adult weighing 75 kilograms (about 165 pounds), far more than most adults take in daily. A 12 ounce can of diet soda usually contains about 192 milligrams of aspartame and a packet of the tabletop sweetener contains about 35mg. An adult weighing 165 pounds would have to drink more than 19 cans of diet soda a day or consume more than 107 packets to go over the recommended level.
Does aspartame cause cancer?
Researchers use 2 main types of studies to try to determine if a substance or exposure causes cancer. (A substance that causes cancer or helps cancer grow is called a carcinogen.)
In studies done in the lab, animals are exposed to a substance (often in very large doses) to see if it causes tumors or other health problems. It's not always clear if the results from these types of studies will apply to humans, but lab studies are the best way to find out if a substance has the potential to cause cancer in humans before widespread exposure occurs.
Another type of study looks at cancer rates in different groups of people. Such a study might compare the cancer rate in a group exposed to a substance versus the rate in a group not exposed to it, or compare it to what the expected cancer rate would be in the general population. But studies in people can sometimes be hard to interpret, because there may be other factors affecting the results that are hard to account for.
In most cases neither type of study provides definitive evidence on its own, so researchers usually look at both lab-based and human studies if they are available.
Studies done in the lab
Many studies have looked for health effects in lab animals fed aspartame, often in doses higher than 4,000 mg/kg per day over their lifetimes. These studies have not found any health problems that are consistently linked with aspartame.
Two studies published by a group of Italian researchers suggested that very high doses of aspartame might increase the risk of some blood-related cancers (leukemias and lymphomas) in rats. However, both the FDA and the EFSA have called these results into question, citing a lack of some important data in the published studies and other concerns.
Studies in people
Most studies in people have not found that aspartame use is linked to an increased risk of cancer.
One early study suggested that an increased rate of brain tumors in the US during the 1980s might have been related to aspartame use. However, according to the National Cancer Institute (NCI), the increase in brain tumor rates actually began back in the early 1970s, well before aspartame was in use. And most of the increase was seen in people age 70 and older, a group that was not exposed to the highest doses of aspartame, which might also make this link less likely. Other studies have not found an increase in brain tumors related to aspartame use.
In the largest study of this issue, researchers from the NCI looked at cancer rates in more than 500,000 older adults. The study found that, compared to people who did not drink aspartame-containing beverages, those who did drink them did not have an increased risk of lymphomas, leukemias, or brain tumors.
A recent study of more than 125,000 people found a link between consumption of aspartame sweetened soda and the risk of leukemia, lymphoma, and multiple myeloma in men, but not in women. Since it also found a link between sugar sweetened soda and lymphoma in men, the researchers concluded that the links they found could be explained by chance.
What expert agencies say
Expert agencies in the United States and elsewhere that have evaluated aspartame have found it safe for use.
The Food and Drug Administration (FDA) regulates the use of aspartame and other artificial sweeteners in the United States. In 2007, the FDA stated:
Considering results from the large number of studies on aspartame's safety, including five previously conducted negative chronic carcinogenicity studies, a recently reported large epidemiology study with negative associations between the use of aspartame and the occurrence of tumors, and negative findings from a series of three transgenic mouse assays, FDA finds no reason to alter its previous conclusion that aspartame is safe as a general purpose sweetener in food.
The European Food Safety Authority (EFSA) assesses the safety of sweeteners such as aspartame in the European Union. According to a 2009 report from its Panel on Food Additives and Nutrient Sources Added to Food:
Overall, the Panel concluded, on the basis of all the evidence currently available… that there is no indication of any genotoxic or carcinogenic potential of aspartame and that there is no reason to revise the previously established ADI for aspartame of 40 mg/kg [body weight].
Though research into a possible link between aspartame and cancer continues, these agencies agree that studies done so far have not found such a link.
Does aspartame cause any other health problems?
Complaints of various health issues have circulated since aspartame first appeared on the market in the 1980s. But for most people, no health problems have clearly been linked to aspartame use.
Phenylketonuria is a rare genetic disorder (present at birth) in which the body can't break down phenylalanine, an amino acid found in many foods. Levels of phenylalanine can build up in the blood, which prevents other important chemicals (like amino acids) from getting to the brain. Unless phenylalanine intake is severely limited, children with PKU suffer from abnormal brain development.
PKU is usually detected in babies by a routine blood test shortly after birth. People with PKU need to follow a phenylalanine-restricted diet. This is especially important in children, whose brains are still developing. It is also important in pregnant women, because it can affect the development of the fetus.
Because phenylalanine is a component of aspartame, it's important that people with PKU limit their intake of aspartame. That is why any product (including medicines) containing aspartame has the warning “Phenylketonurics: contains phenylalanine.”
Other health complaints
Claims have been made that aspartame is related to health effects ranging from mild problems such as headache, dizziness, digestive symptoms, and changes in mood, to more serious health issues such as Alzheimer disease, birth defects, diabetes, Gulf War syndrome, attention deficit disorders, Parkinson disease, lupus, multiple sclerosis, and seizures. However, studies done to date have not found any consistent evidence of harm.
Should I limit my exposure to aspartame?
Aside from the effects in people with phenylketonuria, no health problems have been consistently linked to aspartame use. Research on artificial sweeteners, including aspartame, continues today.
For people who want to avoid aspartame, the easiest way to do this is to check the labels before buying or eating foods or drinks. If aspartame is in the product it will be listed in the ingredients. The product label will also contain the warning “Phenylketonurics: contains phenylalanine.”
In addition to the American Cancer Society, other sources of information and support include:
Food and Drug Administration
Toll-free number: 1-888-463-6332 (1-888-INFO-FDA)
National Cancer Institute
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
Artificial sweeteners and cancer: www.cancer.gov/cancertopics/factsheet/Risk/artificial-sweeteners
*Inclusion on this list does not imply endorsement by the American Cancer Society.
No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.
Council on Scientific Affairs. Aspartame: review of safety issues. JAMA. 1985;254:400-402.
European Food Safety Authority. Opinion on a request from the European Commission related to the 2nd ERF carcinogenicity study on aspartame. 2009. Accessed at www.efsa.europa.eu/en/scdocs/scdoc/945.htm on April 13, 2010.
Flamm GW. Letter to the Editor. J Neuropathol Experimental Neurol. 1997:5:105-106.
Food and Drug Administration. FDA Statement on European Aspartame Study. April 20, 2007. Accessed at http://www.fda.gov/food/ingredientspackaginglabeling/foodadditivesingredients/ucm208580.htm on 4/11/2014
Gallus S, Scotti L, Negri E, et al. Artificial sweeteners and cancer risk in a network of case-control studies. Ann Oncol. 2007;18:40-44.
Gurney JG, Pogoda JM, Holly EA, et al. Aspartame consumption in relation to childhood brain tumor risk: results from a case-control study. J Natl Cancer Inst. 1997;89:1072-1074.
Lim U, Subar AF, Mouw T, et al. Consumption of aspartame-containing beverages and incidence of hematopoietic and brain malignancies. Cancer Epidemiol Biomarkers Prev. 2006;15:1654–1659.
Magnuson BA, Burdock GA, Doull J, Kroes RM, Marsh GM, Pariza MW, Spencer PS, Waddell WJ, Walker R, Williams GM. Aspartame: a safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies. Crit Rev Toxicol. 2007;37(8):629-727.
National Cancer Institute. Artificial sweeteners and cancer. 2009. Accessed at www.cancer.gov/cancertopics/factsheet/Risk/artificial-sweeteners on April 8, 2014.
Olney JW. Farber NB, Spitznagel E, Robins LN. Increasing brain cancer rates: is there a link to aspartame? J Neuropathol Experimental Neurol. 1996:55:1115-1123.
Schernhammer ES, Bertrand KA, Birmann BM, Sampson L, Willett WC, Feskanich D. Consumption of artificial sweetener- and sugar-containing soda and risk of lymphoma and leukemia in men and women. Am J Clin Nutr. 2012 Dec;96(6):1419-28. Epub 2012 Oct 24. Erratum in: Am J Clin Nutr. 2013 Aug;98(2):512.
Soffritti M, Belpoggi F, Tibaldi E, et al. Life-span exposure to low doses of aspartame beginning during prenatal life increases cancer effects in rats. Environ Health Perspect. 2007;115:1293-1297.
Yost D. Clinical safety of aspartame. Am Fam Physician. 1989;39:201-206.
Last Medical Review: May 28, 2014 Last Revised: May 28, 2014