Vitamin D and Calcium Regulation

Mechanism of Vitamin D and Calcium Relationship

Vitamin D helps bones absorb calcium, acting as a critical regulator of calcium and bone homeostasis 1, 2
The active form of vitamin D (calcitriol) controls calcium absorption in the small intestines through a vitamin-D-regulated saturable pathway 1
Vitamin D interacts with parathyroid hormone to maintain calcium homeostasis between blood and bones 1, 2

There are two main sources of vitamin D in the human body: Ergocalciferol (vitamin D2) and Cholecalciferol (vitamin D3) 1, 2
Vitamin D3 is converted to its active form through enzymatic processes in the liver and kidney 1, 2
Most cells contain specific receptors for the active form of vitamin D 1, 2

Insufficient vitamin D leads to impaired dietary calcium absorption 1, 2
When vitamin D is inadequate, the body uses calcium from skeletal stores, which can weaken existing bones 1, 2
The Institute of Medicine defines adequate vitamin D levels as >50 nM (>20 ng/ml) of 25-OH-vitamin D 3

Vitamin D has beneficial effects on muscle strength and balance 1, 2
Current evidence indicates that calcium with or without vitamin D intake from food or supplements has no relationship (beneficial or harmful) with cardiovascular disease risk 4, 5

Calcium intake from food sources is preferred over supplements 5, 6
Supplemental calcium can be safely used to correct shortfalls in intake without cardiovascular concerns, as long as intake doesn't exceed 2000-2500 mg/day 5, 6
For those at risk of low calcium, consumption of 1500 mg/day is recommended to optimize bone health 3
The gut cannot absorb more than 500 mg of calcium at once, so calcium intake should be spread throughout the day 3
Daily maintenance supplementation of 1000-2000 IU vitamin D3 is reasonable for female athletes, depending on sun exposure 3