Announcing the Bone Health Masterclass!

How the Skull Bone Marrow talks to Brain Cells

QUICK TAKES

🦴 Bone and brain are genuinely connected. People with Alzheimer's (AD) are more likely to have osteoporosis, and vice versa — and it's not coincidental. AD alters brain signaling, hormones, and inflammation in ways that directly cause bone loss.

💀 Skull bone marrow is a special immune hub. The skull's bone marrow communicates with the brain through dedicated channels, allowing immune cells to move rapidly into brain tissue. Bone-building activity in the skull regulates this flow, shaping local inflammation, blood flow, and cognition.

📣 Bone-derived signals influence AD directly. Hormones and proteins made by bone and bone marrow affect the key drivers of cognitive decline — amyloid buildup, tau tangles, synaptic health, and immune cell behavior. Notably, genes that raise AD risk are also active in bone cells, linking genetic AD risk with osteoporosis risk.

🩸 Blood flow is where bone and brain health intersect. In AD models, manipulating bone-building cells in the skull changes brain blood flow. Poor bone-building activity correlates with reduced blood flow and worse cognition; boosting it can partially reverse both. Bone and vascular health appear to be two levers on the same system.

🎯 This connection can be measured and potentially treated. Possible interventions include protecting bone health (exercise, medications, vitamin D), targeting bone-derived hormones, and regulating skull marrow immune activity. Future AD trials may track bone markers and imaging alongside cognitive outcomes to test whether treating bone health can slow AD progression.

FAVORITE FINDS

1. Caroline Girvan's strength training programs — free on YouTube, genuinely world-class, and the reason I now have opinions about Bulgarian split squats.

2. Andy Galpin's podcasts — if you want to understand what exercise actually does to your biology, this will give you all the details. In conversation with Andrew Huberman, it’s even better.

3. Stacy Sims's “Lift Heavy S—” Menopause Course — focused on exercise with some diet advice. Not everything in this course is well-proven, but it’s inspiring, and appropriately emphasizes the importance of plyometrics.

4. My bone health workbook — a practical starting point if you want to understand where you stand and what to do about it.

5. My bone health course, launching August 11th, 2026; details and pricing at the link.

6. The articles that inspired this newsletter:

   Liu ZT, Zhang Y, Li X, et al. Crosstalk between bone and brain in Alzheimer's disease: mechanisms, applications, and perspectives. Alzheimers Dement. 2024.pubmed.ncbi.nlm.nih.gov/38824621/
   
   Xiong X, Sun X, Zhang L, et al. A skull bone marrow-to-brain axis links osteoblastic activity to myeloid cell trafficking, cerebral blood flow, and cognition in Alzheimer's progression. Adv Sci (Weinh). 2026. https://pubmed.ncbi.nlm.nih.gov/42107073/
   
   Cugurra A, Mamuladze T, Rustenhoven J, et al. Skull and vertebral bone marrow are myeloid cell reservoirs for the meninges and CNS parenchyma. Science. 2021.
   

DEEP DIVE

Your Skull Is Talking to Your Brain
I have been in functional medicine long enough to know that when two serious diseases keep showing up together, it is not a coincidence. It is a clue.
Osteoporosis and Alzheimer's disease show up together constantly. And for a long time, we wrote it off as downstream frailty — of course people with dementia lose bone. They don't move. They don't eat well. They fall. That should explain it.

New research is telling a very different story.
It turns out the skull bone marrow is in direct, privileged communication with the brain — through specialized vascular channels that bypass the general circulation entirely. The immune cells generated there travel straight into the meninges (membranes surrounding the bran) and brain tissue. And in Alzheimer's models, when that skull marrow is functioning well, so is brain blood flow and cognition. When it isn't, both decline.

Bone is not scaffolding. It is an endocrine and immune organ — the question is whether focusing on bone health might modify Alzheimer's trajectory.

I have written the full story — the science, the molecules, what supports both bone and brain, and what quietly harms them — on my practice website. If this is a topic that matters to you or someone you love, I hope you'll read it.