I've been weight training 3x a week this year for the first time in my life. Reformer Pilates, HIIT, a trainer every other week. Because a DEXA scan at 43 found osteopenia in my hips that I had no idea was there. And because perimenopause is on its way.

Full-body DEXA has become my favorite way to track body composition — it measures lean mass, bone density, and visceral fat all at once. I think everyone should have a baseline by 35. And until recently, it was the only way to track muscle and bone health simultaneously.

Then a 2025 study out of Singapore changed that. Researchers followed 891 midlife women for 6.6 years and found that the ratio of two blood markers — creatinine divided by cystatin C — predicted both muscle loss and bone density decline at the same time. One number. Both systems. From a blood draw.

It turns out muscle and bone aren't independent. Muscle pulls on bone every time it contracts — that mechanical load is what tells your bones to keep building. Less muscle means less stimulus means faster bone loss. Which is why one ratio can capture both.

And that same ratio predicts mortality. Every one-unit increase in CCR is associated with a 17% lower risk of dying from any cause.

Creatinine is already on your standard labs. Cystatin C you have to ask for. Nobody's calculating the ratio routinely today.

This May — National Osteoporosis Awareness and Prevention Month — here's what CCR measures and what to do about it.

If you want your CCR calculated alongside a full body composition workup, this is exactly what we do at Parsley →

Get your CCR. Creatinine is likely already on your last labs. Ask your doctor to add cystatin C at your next draw. Then: creatinine (mg/dL) ÷ cystatin C (mg/L) = your CCR.

For women:

Track it every 6–12 months. Direction matters as much as the number.

Pair it with a full-body DEXA — lean mass, bone density, visceral fat, by region. Together, these two give you the most actionable body composition picture available.

❌ The old assumption: Creatinine and cystatin C are kidney markers. Check them, file them, move on.

✅ The new reality: Their ratio is a proxy for skeletal muscle mass — independent of kidney function — and it tracks directly with bone density and survival.

Creatinine is produced by muscle at a rate proportional to how much functional muscle you have. Cystatin C reflects inflammation and filtration — but not muscle. Dividing them isolates the muscle signal.

Low CCR at baseline predicted lower MRI-measured muscle volumes and slower gait speed 6.6 years later in 891 midlife women — both core criteria for sarcopenia (Menopause, 2025).

In a NHANES cohort of nearly 4,000 adults followed up to 20 years, each one-unit CCR increase = 17% lower all-cause mortality, 20% lower cardiovascular death (Frontiers in Nutrition, 2025). Low CCR doesn't just mean less muscle. It means your body's functional reserve is running low.

Every muscle contraction pulls on bone. That mechanical load signals osteoblasts — bone-building cells — to get to work. Less muscle → less stimulus → faster bone loss.

CCR was significantly positively correlated with bone mineral density at the lumbar spine, femoral neck, and total hip in a cross-sectional study of 2,992 adults ages 50–85 — strengthening with age (Journal of International Medical Research, 2023).

One ratio. Both systems.

Zone 2 and Pilates alone won't move your bone density. You need resistance training at 70–85% of your 1-rep max — heavy enough that the last few reps are hard. That's what triggers bone formation alongside muscle growth.

The RDA of 0.8g/kg prevents deficiency. It doesn't build or protect musculoskeletal tissue. About 30% of bone is protein matrix — you can't rebuild it without the raw material.

3–5g/day of creatine monohydrate combined with resistance training improves lean mass, walking speed, and hip bone geometry in postmenopausal women. A 2025 review flagged the 40s as a critical window to start (JISSN, 2025). Without training, it doesn't move bone. With training, it amplifies the effect.

Your gut microbiome regulates calcium absorption, inflammation, and osteoclast activity — all of which affect how fast your bones break down.

I take Bondia by Sōlaria Biō, a synbiotic studied in a 286-woman RCT that reduced femoral neck bone loss by 85% vs. placebo in women with osteopenia (Osteoporosis International, 2025). I've been on it since my osteopenia diagnosis. Use code STRONGMOM20 for 20% off this Mother's Day.

The goal: a measurable baseline and a protocol that moves it. CCR and DEXA give you that. The rest is consistency.

Does this resonate? Hit reply — I read every response.

This week we went to look at new places to live in NYC. We're contemplating a move.

At almost 45, looking for a new home brings up emotions it didn't used to. This is the place I'll raise my kids through their formative years. The home base for the prime of my life. I'm probably here for 10 years, maybe longer.

When I was younger — before I had a family — I assumed I'd move around a lot. My first NYC apartment was not going to be my last. Wherever I was felt temporary, with a long line of addresses ahead of it. And when we had three kids and found ourselves in a two-bedroom Brooklyn apartment with three young children sharing a room (twin beds and a crib fit nicely!), I was very clear this was not going to work much longer. Like in life, I felt I had a long run ahead of me when it came to real estate.

Now, contemplating a place to actually settle into, I'm aware I'll only live in so many homes from here. The chapters of life architected around children and schools and activities feel more set in blocks. Of course there's no such thing as a sure thing — other moves and adventures may be in my future in ways I can't predict. But the idea of settling into a home base from which to launch into those adventures feels good too.

I'm thinking about the next 10 years of my health the same way. This is the time to double down and invest in the foundation. Muscle, bone, brain, hormones, skin, emotional resilience, spiritual growth. Not a far-off goal — a place I've arrived to inhabit.

"Getting to it later" won't work anymore. That can feel scary when it comes to longevity. I'm choosing to embrace it.

As the only home I'll have for life, the body deserves my utmost care. When I think of it that way, the time to lift weights, the investment in Pilates, and the care I take around food don't feel like a have-to. They feel like decorating my home — making it as comfortable, beautiful, and reflective of me as I can dream of.

I'm making this a place I want to be for a long time. That's healthy motivation.

We just installed a full-body DEXA scanner at Parsley's NYC office in partnership with BodySpec. Lean mass, bone density, visceral fat, body composition by region — open to members and non-members.

Haven't signed up for Parsley yet? You can also ask your Parsley clinician to add cystatin C to your next panel and we'll calculate your CCR baseline together.

Stay strong, stay curious, and breathe,

Robin

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As always, this newsletter is for informational and educational purposes only and is not intended as medical advice. Always consult your healthcare provider before making any health decisions or changes to your treatment plan.