Eight essential nutrients make up the suite of B vitamins also known as the B complex. Research has revealed that these B vitamins influence a vast spectrum of human health and disease. "It's hard to study the B vitamins in isolation," says gastroenterologist Joel Mason. "Four of these B-vitamins cooperate as co-factors in many critical activities in cells in what we call 'one carbon metabolism.'" One of the most active areas for B vitamin research is cognitive health. By the age of 75–80, 40% of people have a diminished ability to absorb food-bound B12, says Mason. This deficiency leads to...