e based a lot of my B12 supplementation recommendations based on the extensive work done by fellow dietitian Jack Norris. He’s my go-to reference when it comes to understanding B12 and his review of the literature is unmatched by anyone I’ve seen. If you really want to understand B12, then I highly recommend clearing your afternoon, pouring yourself a cup of coffee and going down his B12 rabbit hole.
For adults 14 to 64, the RDA 2.4µg per day. However, you need much higher levels of B12 in supplementation to meet those needs as absorption rates drop significantly from higher doses of supplements vs. food. Therefore, the recommendation is to either take 2.0-3.5µg