Does Costco Cause Cancer?

By Alex Tabarrok.

"In December 2025, researchers led by Yazan Alwadi at Harvard’s T.H. Chan School of Public Health published a paper in Environmental Health that claimed to find that cancer incidence increased for people living closer to nuclear power plants in Massachusetts. In March, the same researchers published an expanded nationwide study claiming a similar result—this time looking at cancer mortality rates, rather than incidence—in Nature Communications. This was followed by a paper in the Journal of Exposure Science & Environmental Epidemiology that looked at associations of lung, breast, and colon cancers. Most recently, a study of total mortality, not just cancer, was published in the European journal Environmental Epidemiology.

The problem? Using the same methods pretty much everything causes cancer. An amazing takedown from Deric Tilson and Adam Stein:

For instance, living near a private four-year university is associated with a 15-fold increase in cancer mortality when compared to living near a nuclear power plant.

Costco has the largest effect of all the locations we have tested. Over 2.2 million cancer deaths can be attributed to Costco; that’s more than 20% of all cancer deaths between 2000 and 2018. Hot dogs, bulk spices, and reasonably priced clothes come with a cost.

What went wrong?

[The authors] chose nuclear power plants because a story could be built around that framework. When the researchers got positive results across our nation’s nuclear power plants, they didn’t check what their shiny new methodology would do using other landmarks. This is their pitfall: by taking the easy way out—getting results and making up a story around those results without double-checking their method—the authors could have no idea that what they were actually capturing was the methodology itself.

…The attributable number of deaths from this methodology is probably zero, but the attributable number of bad papers is at least four."

Here are two more excerpts from the Deric Tilson and Adam Stein paper:

"But proximity is not exposure. We have methods of measuring exposure for nuclear power plant workers. While the radiation exposure of nuclear workers will always be greater than or equal to that received by the surrounding public, most of the closely monitored US nuclear workforce receive no measurable annual dose. When workers are exposed to radiation, the average dose received is only 2 percent of the occupational limit. If operators and workers who are on-site at nuclear power plants receive an annual dose between zero and one-fiftieth of the occupational limit, how is it possible that residents 5, 10, 25, 50, 120, or 200 kilometers away would receive any measurable dose from the same plant?"

"In our original rebuttal, we remarked that the studies can’t prove their assertions because they lacked proper control. It seems they also neglected to do any placebo testing. They chose nuclear power plants because a story could be built around that framework. When the researchers got positive results across our nation’s nuclear power plants, they didn’t check what their shiny new methodology would do using other landmarks. This is their pitfall: by taking the easy way out—getting results and making up a story around those results without double-checking their method—the authors could have no idea that what they were actually capturing was the methodology itself. In our replication and expansion, we have shown that choosing a number of sites and landmarks from capitals to warehouse stores can all yield a positive result without any reasonable pathway for American citizens to become exposed to radiation, develop cancer, and then die. The variations are random noise, all sloping in a positive direction. Even when using randomized outcomes, the methodology outputs positive results.

The papers by Alwadi et al. don’t show a novel mechanism by which nuclear power plants meaningfully contribute to cancer mortality; instead, they show an association of data points across 400 km-wide circles. 48,519 square miles, about the size of Mississippi, is a massive area to claim any kind of exposure. Most studies measuring distance-based exposures look at much smaller distances, such as under 10 km (an area of 113 square miles). The methodology is blind, which can be a feature in research areas needing to avoid bias, but in this case it is a bug; it doesn’t understand radiation exposure or dose. All it understands are its inputs: coordinates, proximity, covariates, and cancer deaths. From these, it can give you a number and even a positive result, but it cannot explain why that result exists. It is still an ecological study, one with a sophisticated statistical technique, but not a very useful one."