I understand that vitamin B12 generally is safe even in large doses, however with more and more supplements coming to the market with extremely high doses, does one need to worry?

Thank you for your great question about B12. It is true that many supplements contain B12 because of its impressive benefits for the brain, nerves and energy/metabolism. However, as you point out it is important to consider possible downsides of taking too much of any nutrient. You are correct in stating that B12 is water soluble.