“Her childbearing years are decades behind her, but Barbara Koblin, a 59-year-old L.A. business owner, still takes a prenatal multivitamin. She takes a handful of other supplements too, is careful about her diet and, at the supermarket, buys a few of those products enhanced with added vitamins and minerals. ‘I just made the decision on my own that more is better,’ Koblin says. When it comes to some vitamins, however, too much of a good thing can be a bad thing.”