High vitamin K intake is associated with improved bone health and prevention of osteoporotic fractures. At nutritional doses, both vitamins K1 and K2 may contribute to optimizing bone mineral density; intervention studies suggest a synergistic effect with vitamin D and calcium. At higher intakes, vitamin K was demonstrated to also increase bone strength by improved bone geometry, but this effect was restricted to K2. In this paper we demonstrate that the side chain in K2 vitamins may be regarded as a geranylgeranyl derivative which inhibits osteoclast activation, probably via the inhibition of the mevalonate pathway. Although menaquinone-4 (MK-4) seems to be the obvious form of K2 to be used at pharmacological doses, arguments are provided that menaquinone -7 (MK-7) may be more effective at doses that do not exceed the present recommendations for daily vitamin K intake.