Myth: Calcium alone builds strong bones

Calcium is the raw material, but bone strength depends on much more: vitamin D to absorb it, vitamin K2 and protein to build it into bone, hormones and, above all, weight-bearing activity that tells bone to grow stronger.

Choose Detailed for the fuller picture, or Scientific for mechanisms and study data.

Bone is living tissue, constantly broken down and rebuilt.

The full picture

• Calcium from food is the building material.
• Vitamin D controls how much calcium is absorbed.
• Vitamin K2 activates proteins that bind calcium into bone.
• Protein forms the framework that calcium hardens.
• Movement signals bone cells to build. Bones that are not loaded lose strength.
• Hormones, especially oestrogen, protect bone, which is why loss speeds up after menopause.

What the trials say

Supplements are most useful when they correct a shortfall. A vitamin K2 trial in postmenopausal women slowed the decline in bone density, while a very large vitamin D trial in people who were not deficient found no fewer fractures.

Bone remodelling is governed by the RANK-RANKL-OPG axis, with oestrogen suppressing osteoclastogenesis. Vitamin K-dependent gamma-carboxylation of osteocalcin and matrix Gla protein is required for their function.