Does Costco Cause Cancer?

In December 2025, researchers from Harvard's T.H. Chan School of Public Health claimed in a paper published in Environmental Health that cancer incidence rose among individuals living near nuclear power plants in Massachusetts. In March, the same team published a nationwide study in Nature Communications suggesting a similar result, but this time focusing on cancer mortality rates.

This was followed by a paper in the Journal of Exposure Science & Environmental Epidemiology examining associations with lung, breast, and colon cancers. Most recently, a study on total mortality, not just cancer, was published in the European journal Environmental Epidemiology. However, a detailed analysis by Deric Tilson and Adam Stein reveals that using the same methods, almost any factor could be linked to cancer.

For instance, living near a private four-year university was found to increase cancer mortality by 15 times compared to living near a nuclear power plant. Costco emerged as having the largest effect, with over 2.2 million cancer deaths attributed to it, accounting for more than 20% of all cancer deaths between 2000 and 2018. The researchers chose nuclear power plants because they felt they could build a compelling narrative around that framework.

Once they obtained positive results near these power plants, they did not verify if their method would yield similar results when applied to other landmarks. This oversight may explain why the authors could not realize that their methodology was capturing the method itself rather than actual cancer-causing factors. Consequently, the number of deaths attributable to this methodology might be close to zero, but the number of flawed studies could be at least four.