In one study, scientists randomly assigned 5,442 women to take high daily doses of vitamin B-6 (50 milligrams), vitamin B-12 (1,000 micrograms), and folic acid (2,500 mcg), or a placebo. After seven years, the risk of bone fractures was no lower in the B vitamin takers. In another study, researchers randomly assigned 95 people with debilitating fatigue and irritable bowel syndrome or inflammatory bowel disease to take vitamin B-12 (1,000 mcg a day) or a placebo. After eight weeks, fatigue was no lower in the B-12 takers.