What exactly does it mean to have too low cholesterol?

Very Little: Once upon a time, we thought that having too little cholesterol could interfere with the formation of hormones like testosterone and estrogen, or alter the membranes surrounding cells. None of that has really borne out, and for heart attack patients we routinely target an LDL of 50-70. Odds are pretty good that you're just lucky and have a good diet and good genes.