Anything over 2000 mg a day has the potential for some side effects in some people, but you should have no problems on 1500-2000 mg everyday, regardless of your predisposition. Studies have shown that an optimal intake of calcium (about 1500 mg a day on average, which most people do NOT get), can increase insulin sensitivity, speed up fat loss (this effect is more pronounced in women), and can help inhance athletic performance.