The researchers assigned patients at random to take either a pill that contained vitamins and minerals or a placebo pill every day for 1 year. The vitamin and mineral pill contained amounts of vitamins and minerals similar to those found in most commercially available multivitamin and mineral supplements. The placebo looked, smelled, and tasted like the supplement but contained only calcium, magnesium, and vitamin B2. The researchers then followed patients for 1 year and asked them to record in a diary any infections they developed and the number of days they missed work because of an infection. They also asked patients about their physical and mental health, using a standard survey.