I had heard about this before, but what was actually shocking for me is that the risk is increase already with rather low intakes of 55 micrograms a day orally (over several years). https://www.theatlantic.com/health/...d20aa_ta&utm_medium=social&utm_source=twitter 55 micrograms orally means that about 4-5 micrograms are actually absorbed. Absorption is very low above 2.5 micrograms which are absorbed via intrinsic factor. Above that, only 1-3% is absorbed via passive diffusion. When I now think that many (including me) are taking regular injections of 1000 micrograms and more, that makes me worried. Of an injection, bioavailability is 30-70% (depending on the kind of B12 - cyano/hydroxo/methyl/adenosylcobalamin - and method of injection, i.e. intramuscular vs subcutaneous vs intravenous). So that may be 100 times the dose that already doubled lung cancer risk I'm of course not telling anyone to stop B12, especially if it helps. But I think being aware of this potential risk is important.