In a supplement industry awash in the latest “superfruits” and “miracle foods,” the long-time nutritional workhorses tend to get the short shrift. Compared to flashy compounds and foods with exotic-sounding names—resveratrol, acai berry, camu camu—it’s all too easy to overlook something as ho-hum as magnesium. But there’s a reason—many reasons, in fact—why magnesium is a…