The question "What does choline do" is a complex one. Once it enters the body, it can be directed toward several very different jobs. It can help build cell membranes, become the neurotransmitter acetylcholine, or e converted into betaine and contribute methyl groups to the methylation cycle.

Your body actually has two major pathways for recycling homocysteine back into methionine. One depends primarily on folate and vitamin B12. The other uses choline-derived betaine.