Across 16 randomised trials in postmenopausal women, vitamin K2 modestly improved lumbar-spine bone density; its effect on fracture risk was not significant overall and only reached significance after one inconsistent trial was excluded.
Small, one-off gains in bone density that are unlikely to reduce fractures on their own.
In older adults, progressive resistance training increased hip/femur bone density, though the lumbar spine showed no significant change and the bone-density result was far less consistent than the strength gains.
On its own it does not prevent fractures in people who are not deficient (36 trials, 92,000 people); with calcium the benefit is small.
