Windmill Natural Vitamins Magnesium Citrate 400 mg in 2 tablets (1 serving). Magnesium Citrate offers a high potency of the essential mineral magnesium in its highly absorbable citrate form. Essential for calcium metabolism, the production of enzymes and proteins. Windmill offers cutting edge, clinically based formulas to satisfy a variety of market needs, including multi and single vitamins and minerals, whole food supplements, greens, proteins, specialty formulas, anti-aging nutrition, condition specific, performance nutrition, and herbals.