Combining vitamin D with vitamin K for bone health Original paper

Vitamin D and vitamin K (both K₁ and K₂) play a role in bone health. Yet in studies on bone density, their combined supplementation has produced mixed results.

It was a meta-analysis of 8 randomized controlled trials lasting from 6 months to 3 years (for a total of 971 participants, mostly female). The daily doses ranged from 1 to 10 mcg (40–400 IU) of vitamin D, 100 to 1,000 mcg of K₁, and 100 to 45,000 mcg of K₂.

Overall, moderate-quality evidence indicated that a combination of vitamin D and vitamin K can improve bone mineral density. A secondary analysis indicated that K₂ may be better than K₁ for that purpose. A limitation is that the meta-analysis was not able to account for the baseline D and K levels of the participants.

While K₁ is widely available from plant-based foods, K₂ (which is found mostly in bacteria and animal tissues) is present in fewer foods, such as liver, cheese, sauerkraut, and nattō (fermented soybeans).