Stop obsessing over your sleep score: Doctor shares 4 metrics that can actually predict how long you'll live

Longevity may depend more on aerobic fitness, muscle function and visceral fat than daily step counts or wearable scores, says a sports medicine physician.

If you're checking your sleep score, and step count every morning like it's a ritual, you're not alone. But the longevity doctors who study how to stay healthy for decades? They say you may be obsessing over the wrong numbers.

In an interview with HT Lifestyle, Dr Mukul Mittal, sports medicine physician and medical director at Ultrahuman, talked about what actually predicts healthspan — the number of years you live without chronic disease — and most of it isn't on your annual blood report or your wearable dashboard. Here’s what actually matters, according to him.

1. Your cardio fitness matters

If Dr Mittal had to pick just one number to predict your future health, it wouldn't be steps or calories: "If I could measure only one thing about a person's long-term health, it would be cardiorespiratory fitness. VO2max is one of the strongest predictors of all-cause mortality."

Translation: how efficiently your body uses oxygen when you're pushing hard. Research on large treadmill cohorts found that people in the lowest fitness category had a mortality risk that was comparable to — or even worse than — smoking or having diabetes, he explained. The best part? It's fixable. "The good news is that it is highly trainable at almost any age," Dr Mittal said.

2. How you move is important

At elite performance labs, they even use force plates to measure power output. Why? Because you lose power years before you notice you can't climb stairs easily. "Strength asymmetries and power loss show up years before someone notices a problem climbing stairs," he noted.

3. Where you store fat matters too

Your BMI could be totally 'normal' and you could still be at risk, especially for south Asians. "The third is where you carry fat, not how much you weigh. We routinely see the 'thin-fat' phenotype: normal weight, normal-looking reports, but high visceral fat on a DXA scan. BMI misses these people entirely," Dr Mittal shared. This is visceral fat — the fat wrapped around your organs — not the kind you can pinch. A DXA scan catches what the scale misses.

4. Your standard blood work misses real red flags

That basic annual panel? It doesn't tell the full metabolic story, Dr Mittal shared. He said to look at these instead:

⦿ ApoB: "ApoB counts the particles that actually drive arterial plaque, and it often reveals risk that LDL cholesterol hides."

⦿ Lp(a): "Lipoprotein(a) is largely genetic, needs to be tested only once in a lifetime, and is elevated in a substantial share of Indians."

⦿ Fasting Insulin + HbA1c: Together they catch blood sugar issues yearsbefore your glucose goes abnormal.

So, are wearables useless?

Dr Mittal said your ring and watch are amazing for one thing: trends. "A ring or watch is excellent at trends. Where wearables fall short is absolute accuracy," he said. Your ring's sleep stages? "A reasonable estimate, not a sleep study," he said. Your watch's VO2max? "Modelled from heart rate and movement, and in validation studies they can be off by a meaningful margin," he added. And blood tests have the opposite problem: "A blood test is a snapshot of one morning."

Even trendy tests like biological age clocks and DNA risk scores often aren't validated in diverse populations, including those of Indian ancestry, he added. According to him, clinical tests tell you where you stand. Wearables tell you which direction you're moving and why. Put them together, and they point to the same boring-but-true formula: aerobic exercise, lift heavy things, sleep consistently, and keep visceral fat in check. No smart ring can do that for you.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.