Six proteins may link BCAAs to heart disease risk

Ischaemic heart disease remains the leading cause of illness and death worldwide, so understanding which circulating molecules push risk up or down has real value. Branched-chain amino acids — leucine, isoleucine and valine, familiar to anyone who has read a supplement label — have repeatedly been associated with higher ischaemic heart disease risk in observational work. What has been missing is any clear account of why. Without a plausible biological pathway, an association between a blood metabolite and a disease is hard to interpret and even harder to act upon. This study set out to fill that mechanistic gap.

The researchers used a two-step, proteome-wide Mendelian randomisation design, which uses inherited genetic variants as stand-ins for lifelong exposure to higher or lower BCAA levels. In the first step they tested genetic proxies for BCAAs against 2,922 proteins measured in the UK Biobank Pharma Proteomics Project, supplemented by a meta-analysis with data from deCODE. In the second step they tested whether those BCAA-linked proteins were themselves associated with ischaemic heart disease, using CARDIoGRAMplusC4D with 122,733 cases and 424,528 controls, and replicating in FinnGen with 31,640 cases and 187,152 controls. Sensitivity analyses used alternative genetic instruments from deCODE.

Genetic proxies for BCAAs were associated with 40 proteins across the proteome. Of those, six showed consistent evidence of mediating the BCAA–heart disease relationship: complement component 1s, coagulation factor II, granulin, PCSK9, sex hormone-binding globulin and V-set and transmembrane domain-containing protein 2 like. Mediation analysis suggested these proteins together accounted for between 6.5% and 32.1% of the association between BCAAs and ischaemic heart disease risk. The authors report that all associations held up across different analytical methods and replicated in independent datasets. The implicated proteins span inflammation, coagulation, lipid metabolism and cellular stress response, rather than a single tidy pathway.

Observational studies had already flagged BCAAs as a marker of higher cardiovascular risk, but the mechanism was unresolved and the direction of causality contested. This analysis extends that literature by naming specific candidate intermediaries, and the appearance of PCSK9 — a well-known lipid regulator — anchors the finding in familiar cardiovascular biology. Even so, the mediated fraction is partial, leaving most of the association unexplained. Mendelian randomisation reduces some confounding but cannot capture dietary intake, timing or dose, and it says nothing about what happens when someone takes a BCAA supplement. Whether lowering BCAA exposure would shift these proteins in practice remains untested.

This is a reason to think the BCAA–heart disease link is not merely a statistical curiosity, but has plausible biology behind it involving inflammation, clotting and lipid handling. It is not evidence that a BCAA supplement causes heart disease, nor that avoiding protein-rich foods lowers risk — genetic proxies for lifelong metabolite levels are a very different thing from what you eat this week. For readers who take amino acid products, the honest summary is that the mechanistic story is becoming clearer while the practical implications remain unsettled. It is a research signpost, not a dietary verdict.