Beyond Bone Health: Exploring the “Heart–Brain–Bone” Axis Modulated by Lipid-Soluble Nutrients (Omega-3, Vitamin D3, and Vitamin K2)

Background: Population aging is driving a convergent rise in three disorders historically managed in isolation: cardiovascular disease, neurocognitive decline, and osteoporotic bone loss. Accumulating mechanistic data indicate that these systems are coupled through shared regulators of calcium trafficking, inflammation resolution, vascular integrity, and inflammaging, supporting the concept of an integrated "Heart-Brain-Bone" axis. Three lipid-soluble nutrients-long-chain omega-3 polyunsaturated fatty acids (EPA/DHA), vitamin D3 (cholecalciferol), and vitamin K2 (menaquinone-7 [MK-7])-act on overlapping nodes of this network. Methods: We conducted a structured narrative review of mechanistic, observational, and randomized controlled trial (RCT) evidence, grading the strength of support for each claim. Results: Vitamin K2-dependent gamma-carboxylation of matrix Gla protein (MGP) and osteocalcin is proposed to reciprocally direct calcium away from the arterial wall and toward the bone matrix, offering a candidate mechanistic resolution of the "calcium paradox" associated with isolated vitamin D3 supplementation; EPA/DHA-derived specialized pro-resolving mediators may support resolution of endothelial and neuronal inflammation; and bone-, vascular-, and brain-derived signals (osteocalcin, FGF23, the neurovascular unit) interconnect the three organs. Human clinical evidence, however, is heterogeneous and formulation- and population-dependent: cardiovascular omega-3 RCTs are discordant (REDUCE-IT, which used icosapent ethyl [an EPA ethyl ester], positive; VITAL/STRENGTH/ASCEND null, predominantly in lower-risk or replete cohorts), cognitive trials are largely null or subgroup-dependent (MAPT, DO-HEALTH), and MK-7 improves surrogate bone and calcification biomarkers, with only a single recent hard-endpoint coronary calcification RCT (VitaK-CAC). Conclusions: The combined use of long-chain omega-3, vitamin D3, and MK-7 is mechanistically rational and hypothesis-generating rather than clinically established; benefit appears most plausible in individuals with elevated risk or demonstrable nutritional insufficiency, and least in replete, low-risk populations. Findings should be interpreted within a broader healthy-aging context that includes lifestyle and psychosocial factors. Adequately powered factorial RCTs stratified by baseline Omega-3 Index, 25(OH)D, and vitamin K status, with prespecified mechanistic biomarkers and hard endpoints, are required.