The Two Most Powerful Predictors of How Long You’ll Live (And Why They Matter More After 40)

Susan Chapman Tomlinson
Jan 5
4 min read

If you asked most people what determines how long they’ll live, you’d probably hear answers like genetics, luck, or maybe cholesterol numbers. For years, I believed that too. I thought aging was mostly out of our control and that slowing down, gaining weight, and losing strength were just part of the deal.

But science tells a very different story.

Research now consistently shows that two factors predict longevity more than almost anything else especially for women in midlife and beyond. And the good news? Both are highly trainable, even later in life.

Those two predictors are muscle mass and metabolic health.

Let’s talk about why they matter so much and why understanding this changed everything for me in my 60s.

Predictor #1: Muscle Mass & Strength

Muscle is often misunderstood, especially for women. For decades, we were told to focus on being smaller, lighter, and thinner. Muscle was treated like a cosmetic bonus — not a biological necessity.

The truth is, muscle is one of the most powerful longevity organs in the body.

As we age, we naturally lose muscle through a process called sarcopenia. That loss accelerates after 40 and speeds up even more during menopause. Without intervention, many women lose up to 30–40% of their muscle mass by their 70s.

Why does that matter?

Because muscle does far more than help you move.

Healthy muscle:

Increases resting metabolism (you burn more calories at rest)
Regulates blood sugar by pulling glucose out of the bloodstream
Protects joints and bones, reducing fracture risk
Produces anti-inflammatory signaling molecules
Supports balance and coordination, lowering fall risk
Plays a role in hormone signaling and brain health

Studies consistently show that people with higher muscle mass and better strength live longer — regardless of their weight or BMI. Grip strength alone has been linked to lower all-cause mortality.

In simple terms: Muscle keeps you alive longer and functioning better while you’re here.

Predictor #2: Metabolic Health (Insulin Sensitivity)

The second major predictor of lifespan is how well your body manages energy specifically insulin sensitivity.

Metabolic health determines how efficiently your body:

Uses glucose for fuel
Stores or releases fat
Manages inflammation
Supports brain and cardiovascular health

When insulin sensitivity is strong, your body can switch between burning carbs and fat smoothly. When it’s impaired, fat becomes “locked,” inflammation rises, and energy crashes become common.

This is where many women get frustrated.

They’re eating well. They’re exercising. They’re doing “all the right things.”

Yet fat — especially visceral fat around the abdomen that refuses to budge.

That’s not a willpower problem. That’s a signaling problem.

Poor metabolic signaling is strongly associated with:

Type 2 diabetes
Heart disease
Stroke
Alzheimer’s
Certain cancers
Accelerated aging

You can be thin and metabolically unhealthy. And you can weigh more and be metabolically resilient.

Which is why scale weight alone tells us almost nothing about longevity.

Why These Two Predictors Are Deeply Connected

Muscle and metabolic health don’t operate in isolation.

Muscle is one of the body’s largest glucose-disposal organs. The more responsive your muscle tissue is, the better your insulin sensitivity becomes. And the better your insulin sensitivity, the easier it is to build and preserve muscle.

This creates either:

A downward spiral (muscle loss → metabolic slowdown → fat gain → inflammation)
Or an upward spiral (muscle signaling → metabolic efficiency → fat loss → vitality)

The difference isn’t effort. It’s cellular communication.

The Missing Piece: Cellular Signaling as We Age

Here’s what most wellness conversations leave out:

As we age, the problem isn’t just that we need to “try harder. ”It’s that our internal signals weaken.

The pathways that tell your body to:

Build muscle
Burn fat
Recover efficiently
Repair tissue

…become quieter with time, stress, hormonal shifts, and inflammation.

That’s why doing the same workouts or eating the same way doesn’t work at 55 or 60 the way it did at 35.

Your body still knows how to respond it just needs clearer signals.

My Personal Experience at 61

I want to share this part honestly, because it matters.

At 60, I wasn’t trying to chase youth or extremes. I wanted strength. Energy. And a body that felt responsive again.

Despite staying active and eating well, I noticed:

Muscle was harder to maintain
Fat loss felt stalled
Visceral fat around my midsection was stubborn
Recovery took longer

That’s when I learned about bioactive precision peptides — not synthetic or injectable peptides, but naturally derived peptides designed to support the body’s own communication systems.

What stood out to me wasn’t hype it was how they worked with the body instead of forcing it.

Over time, something shifted.

My muscle responded again.My metabolism felt more efficient. And I saw a reduction in visceral fat not from restriction, but from improved signaling.

At 60, I was able to gain lean muscle and reduce visceral fat because my body finally had the signals it needed to do what it was designed to do all along.

The Bigger Picture

Longevity isn’t about punishment, starvation, or endless cardio.

It’s about: