The Brain-Heart Axis
For a long time, we've talked about the heart and the brain as if they belong to two different conversations — one about circulation, one about cognition and emotion. Cardiology over here, neurology over there.
But that separation was always a little artificial. And the more we learn, the clearer it becomes: the heart and the brain are in constant, two-way communication — a relationship researchers now call the brain-heart axis.
This month, we're unpacking what that means, what the current science actually supports, and why it matters for women navigating hormonal change across the lifespan.
It's worth saying upfront: the brain-heart axis is just one piece of a much bigger picture. Our organs and body systems are increasingly understood to be in bidirectional and multidirectional conversation with each other — the gut, the immune system, the endocrine system, and more, all communicating in ways we're only beginning to map. That bigger picture is a topic for another day. For now, we're focusing in on one relationship: the one between brain and heart.
The heart has its own nervous system
Here's something that surprises most people: the heart contains its own intrinsic network of neurons — sometimes referred to as the heart's "little brain." This means the heart doesn't just passively receive instructions from the brain. It sends signals back, continuously, shaping how the brain interprets emotional and physiological states.
This is what makes the relationship bidirectional rather than one-directional. The old model — brain commands, heart obeys — doesn't capture what's actually happening. It's closer to an ongoing conversation than a chain of command.
Our thoughts and emotions genuinely shape heart function
This bidirectionality has a practical implication: emotional and mental states influence heart rhythm and vascular function, not only the other way around.
This is part of why chronic stress is increasingly understood as a genuine, independent cardiovascular risk factor — not merely a "mental health" issue that sits in its own separate category. The nervous system pathways connecting sustained stress to blood pressure, vascular tone, and heart rhythm are well documented. Mental and cardiovascular health aren't adjacent systems we manage separately — they're mechanistically linked.
Where heart rate variability fits — and where it doesn't
One measurable piece of this brain-heart conversation is heart rate variability (HRV) — the variation in time between heartbeats, reflecting autonomic nervous system activity.
HRV is a legitimate and well-established measure in mainstream medicine. It's used clinically in contexts like risk stratification after cardiac events and assessment of autonomic nerve function, and it's widely used in research examining the links between stress, autonomic regulation, and cognitive load.
Where it gets murkier is outside the clinic. Consumer wearables have popularised HRV as a simple daily "score" — a single number to optimise, like a step count. That framing oversimplifies what is actually a complex, context-dependent physiological signal. The science behind HRV is sound; it's the reduction of it to a daily grade that doesn't hold up to scrutiny.
Shared biology, not just shared timing
Beyond direct neural signalling, the heart and brain are connected through shared risk pathways: inflammation, vascular health, and blood pressure regulation affect both organs simultaneously. This is part of why cardiovascular risk factors in mid-life are now understood to matter for long-term brain health too — the two systems don't just sit near each other; they share underlying biology.
Why this matters differently for women, across every life stage
This is where it gets particularly interesting — and still under-researched.
For women, this brain-heart interplay is nuanced and intertwined with shifts in sex hormones — through puberty, across the menstrual cycle, and through perimenopause and menopause. Oestrogen has protective effects on both the cardiovascular system and the brain, which is part of why hormonal transitions represent meaningful windows for these two systems, rather than isolated events affecting one system or the other.
But here's the honest part: the science is still catching up. There are real, acknowledged gaps in what's known — particularly around how hormonal changes across a woman's lifespan shape this brain-heart relationship specifically. Much of the foundational cardiovascular and neurological research historically under-included women, so some of what we think we know is extrapolated rather than directly studied in female physiology.
Knowing — and naming — what we still don't know is the first step toward new knowledge.
The takeaway
The heart is not just a pump, and the brain is not just a processor sitting above it giving orders. They're in ongoing, bidirectional dialogue — one shaped by thoughts, emotions, stress, inflammation, and, for women, by hormonal shifts across the entire lifespan.
Understanding this connection doesn't give us all the answers yet. But it does change the questions we should be asking — about stress, heart health, brain health, and how differently these systems may behave for women across different life stages.
And it gives us something hopeful and practical to hold onto: if brain and heart are this closely connected, then lifestyle behaviour change becomes a genuine, evidence-based intervention — one set of daily choices with the potential to support both systems at once.
I am Dr Ivana — GP, Lifestyle Physician, and a woman.
