A major difference between boiled and filtered coffee is that the boiled version contains up to 80 times as much coffee-specific fatty acids. These fatty acids have previously been shown in animal experiments to inhibit the growth of cancer.
By comparing filtered coffee and boiled coffee in the Västerbotten Intervention Project (64,603 participants), researchers at Umeå University have been able to show for the first time that various brewing techniques can lead to different risk patterns for cancer. For total cancer, prostate cancer, colorectal cancer, and many other less common forms of cancer, there was no correlation.
Among women who drank boiled coffee more than four times a day there was a lowered risk of breast cancer compared with women who drank coffee less than once a day. Among women who drank filtered coffee there was an increased risk for early breast cancer (under 49 years old) and a decreased risk for late breast cancer (over 55 years old).
Boiled-coffee drinkers, but not filtered-coffee drinkers, also had an increased risk of pancreatic cancer and lung cancer among men.
The study, recently published in the scientific journal Cancer Causes and Control, is the first in the world to compare the consumption of coffee prepared with two brewing techniques in regard to cancer.
Lena Maria Nilsson, Ingegerd Johansson, Per Lenner, Bernt Lindahl, Bethany Van Guelpen. Consumption of filtered and boiled coffee and the risk of incident cancer: a prospective cohort study. Cancer Causes & Control, doi: 10.1007/s10552-010-9582-x.