Calcium

When low (hypocalcemia):

Supplements:

• Calcium Citrate -- 500-1000mg/day (split doses, better absorbed than carbonate; take with meals)
• Vitamin D3 -- 5000 IU/day (essential for calcium absorption; deficiency is the most common cause of low calcium in athletes)
• Vitamin K2 (MK-7) -- 100-200mcg/day (directs calcium to bones, prevents arterial calcification)
• Magnesium -- 400mg/day (required for calcium metabolism and PTH function)

Lifestyle:

• Increase dietary calcium: dairy, fortified plant milks, sardines, leafy greens
• Check Vitamin D levels -- correct deficiency first as it drives calcium absorption
• If on AI (Anastrozole/Exemestane), low estradiol can impair calcium homeostasis long-term

When high (hypercalcemia):

• Rare in athletes -- investigate parathyroid function (PTH), excessive Vitamin D supplementation, or malignancy
• Reduce Vitamin D and calcium supplementation if over-supplementing
• Increase fluid intake to promote renal calcium excretion
• Persistent hypercalcemia warrants endocrinology referral

References:

• Yao, P., Bennett, D., Mafham, M., et al. (2019). Vitamin D and calcium for the prevention of fracture. JAMA Network Open, 2(12), e1917789. DOI: 10.1001/jamanetworkopen.2019.17789
• Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266-281. DOI: 10.1056/NEJMra070553
• Institute of Medicine. (2011). Dietary reference intakes for calcium and vitamin D. National Academies Press. DOI: 10.17226/13050