Caitlin Raymond: Does Drinking More Calcium and Magnesium Every Day Raise the Calcium in My Blood?
Caitlin Raymond, Assistant Professor of Pathology and Transfusion Medicine at University of Wisconsin-Madison, shared on LinkedIn:
“Here’s what happens when you’re a transfusion medicine physician who just moved to hard-water country: you spend a Saturday afternoon thinking about your kettle’s descaling schedule as a physiology problem.
The question: does drinking more calcium and magnesium every day actually raise the calcium in my blood?
The answer took me into parathyroid hormone, bone resorption markers, and a decade of epidemiologic fracture data.
What I found:
- Serum calcium doesn’t budge — homeostasis defends its set point regardless of what’s in your tap water
- The real signal isn’t in blood, it’s in bone: harder water regions show meaningfully lower fracture rates in both kids and older adults
- Calcium supplementation, on its own, barely moves bone density in adults — so the fracture story probably isn’t a calcium story at all
- Magnesium has a more promising, still-unproven mechanism: lowering PTH, shifting the bone formation/resorption balance
- Two minerals, one label (‘hard water’), and probably two separate biological stories tangled together
If you’ve ever wondered whether where you live is quietly shaping your skeleton, this one’s for you. Link to the blog in the first comment.
What’s your local water like — would you guess hard or soft?”

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