Bone-related diseases are a global health problem. The prevalence of osteoporosis and fractures are increasing worldwide, particularly in postmenopausal women. Proper nutrition is crucial for the support of bone health, with calcium typically in the limelight. However, other vital nutrients are necessary for calcium regulation and healthy bone formation and mineralization, including vitamins D and K.

Vitamin D is a fat-soluble vitamin that can be synthesized through a person’s skin when exposed to sunlight or through dietary consumption of fatty fish, dairy products, and eggs. Vitamin D regulates calcium metabolism by increasing intestinal calcium absorption, therefore supporting bone matrix formation and maturation.

Vitamin K is a fat-soluble vitamin that exists in two forms: K1 and K2. Vitamin K1, or phylloquinone, is primarily found in green leafy vegetables. Vitamin K2, or menaquinone, is found mainly in fermented foods (i.e., cheese and natto) or animal products; it is endogenously synthesized by the gut microbiome. Osteocalcin and matrix GLA protein (two vitamin K-dependent proteins) require vitamin K for carboxylation to support bone health. Osteocalcin is synthesized by osteoblasts (bone-building cells) that bind with hydroxyapatite to promote bone mineralization and increase bone strength.

Suboptimal vitamin K2 levels may result in a higher proportion of undercarboxylated osteocalcin, which may be associated with lower bone mineral density (BMD). A systematic review and meta-analysis of 6,425 women concluded that postmenopausal, osteoporotic women receiving vitamin K2 supplements showed a significant increase in lumbar spine BMD and a significant reduction in fracture incidence compared to women who did not receive vitamin K2 supplements.

In addition to their unique roles in supporting bone health, in vitro, animal, and human studies suggest a synergy between vitamins D and K. Vitamin D may promote the production of vitamin K-dependent proteins and, in turn, may promote bone formation. In vitro studies suggest that the active form of vitamin D in the body may increase the osteoblast-specific gene expression of osteocalcin.

A comprehensive meta-analysis of eight randomized controlled trials with a total of 971 subjects revealed that individuals consuming both vitamins D and K had significantly increased total BMD with a significant decrease in undercarboxylated osteocalcin. The researchers further concluded that vitamin K2 improved BMD and bone quality better than vitamin K1.

A Norwegian population study (n = 1,318) of older adults was conducted with an 8.2-year follow-up. The individuals who had low concentrations of vitamins D and K were associated with a greater hip fracture risk than those who had high concentrations of vitamins D and K.

The results of numerous randomized controlled trials that ranged in duration from 8 weeks to 3 years are suggestive of a combined clinical benefit of vitamins D and K in postmenopausal women. However, proper nutrition for bone health is also relevant for older men. One in five men will experience an osteoporotic fracture during their lifetime.

Research suggests that vitamins D and K work synergistically to support bone health. Supplementing vitamins D and K concomitantly may help promote healthy bone strength, formation, and mineralization.

By Danielle Moyer, MS, CNS, LDN