Bone Density Score: The One Number Where Higher Is Better

A bone density report usually isn't something I'd weigh in on. That's typically your primary care doctor's territory. It's also the one lab value where the number you actually want is the opposite of almost everything else I write about here. But I see patients every day who are worried about the interaction between coronary calcium deposition and the first line of defense against osteoporosis - calcium supplementation. Plus I recently underwent my own first-ever bone scan and the report was not exactly written in plain English. So it seemed like a topic I might be able to say a few helpful words about.

What Is a Bone Density T-Score?

A T-score compares your bone density to that of a healthy 30-year-old adult at peak bone mass, not to other people your age, and it comes from a DEXA scan, a low-dose X-ray of your lower spine and hip. 

A T-score of -1.0 or above is normal. Between -1.0 and -2.5 is classified as osteopenia, lower than that young-adult benchmark but not low enough to be classified as osteoporosis. -2.5 or below is osteoporosis. The T-score number is a standard deviation, so a -2.5 means your bone density sits two and a half standard deviations below that healthy reference point, and unlike almost every other number on your chart, lower is not better.

“Standard deviation” is not necessarily an easy concept to appreciate, so I tried to find a visual representation to better illustrate this.  In this graph, the curve represents the distribution of possible bone density readings. The peak of the curve falls at the bone density expected for a healthy 30 year old and the more you deviate leftwards away from the peak, the greater the difference between your bones and that of that 30 year old. 

What the graph makes clear is that by the time you get to a T-score of -2.5, your bone density is far from healthy - and looks very, very different from that of a young person.  The bones of a healthy 30 year old are unlikely to crumble with a minor injury.  Bones with a T-score of -2.5 or lower are at high risk.  

What is a Z-Score?

Rather than comparing your bone status to a healthy 30 year old, a Z-score lets you know how you compare to the average peer of the same age, sex, size and ethnicity.  It’s also presented as a standard deviation number. -2.0 or lower Z-score indicates a significantly lower bone density than expected compared to your peers.  

Z-scores are most useful in children, premenopausal women, and men under the age of 50. These individuals might undergo DEXA scanning because they've suffered an unusual fracture, or because they have a health condition that might put them at risk of developing osteoporosis. A low Z-score does not necessarily mean that someone has osteoporosis. Rather, it serves as a red flag for underlying conditions that impact bone health - like vitamin D deficiency, long term steroid therapy or hormone issues. 

Why Does Bone Density Decline With Age?

Bone is constantly being broken down and rebuilt, and estrogen helps keep that balance in check.

That's why bone loss speeds up for women in the years around menopause, often faster than at any other point in life. It's the same hormonal shift behind the cholesterol changes I wrote about a few weeks ago, just acting on a different tissue. Once estrogen drops, breakdown starts outpacing rebuilding, and bone density falls. And honestly, this is where post-menopausal hormone therapy may have its greatest positive impact - helping maintain bone density.  

Does Losing Bone Density Affect Your Heart?

No. Even though calcium scores in coronary arteries tend to rise as bone weakens, the two are not related. 

The two processes do share similar drivers: the same estrogen decline, plus inflammation and signaling pathways that affect bone and blood vessels together. And… the same physical inactivity.  But there is no calcium speedily moving from your skeleton into your arteries.

It’s also not calcium being forced into your arteries by calcium supplements. Just like you can’t expect to build muscle by simply eating more protein (you need to exercise for that protein to enter your muscles), you can’t calcify your arteries by taking in more calcium. Artery calcification is an active process.  Meaning there needs to be a reason for calcium to enter arteries. I covered why calcium in artery walls isn't automatically the dangerous part in another blog. 

Should You Worry About a Low T-Score?

Not automatically. A T-score is one input, not the whole picture.

Fracture risk also depends on multiple factors including your age, prior fractures, whether you smoke, drink, and your risk of falling, which is why the same T-score means something different in different people. FRAX is the tool that pulls those factors together to estimate real fracture risk, and it's usually what ultimately guides the medication conversation, not the T-score alone.

The World Health Organization developed the FRAX Calculator to help doctors decide if patients should be considered for medications or lifestyle changes alone. FRAX  estimates your 10 year risk for experiencing a fracture in a major bone, like your shoulder, spine or wrist.  It separately estimates the risk of a hip fracture as well. It is most useful for postmenopausal women and men aged 50 or older who have osteopenia.

Exercise and calcium supplementation alone are generally recommended if the 10 year general fracture risk is less than 20% and hip fracture risk falls below 3%.  If general fracture risk is 20% or greater - or if hip fracture risk is 3% or higher - a medication discussion is likely to follow.

What Actually Helps Bone Density?

Moving your body! But not all exercise counts equally.  Weight-bearing exercise, especially, is proven to slow bone loss.

Walking, stair climbing, and resistance training load your bones enough to stimulate new growth. Swimming and cycling are great for your heart, but they don't load your skeleton the same way, so they do less for bone density. Gentle balance type activities - such as Tai Chi - are an excellent addition. Not so much for building bone strength but for making you less likely to fall in the first place.  Calcium and vitamin D matter too, both through food, and supplements if your doctor recommends them.

If your score lands in the osteopenia or osteoporosis range, that's a reason for a conversation with your doctor, not a reason to panic. Medication is sometimes the right call, and that's not a failure any more than needing medication for cholesterol is.

Calcium intake is also important, but so is the overall quality of your diet. And you don’t have to pick your bones or your heart.  You can take care of both together.  Calcium is not just found in milk and cheese (although these are great sources). Broccoli, kale, collard greens, brussels sprouts, dried figs, almonds and chia seeds also deliver calcium. So if you’re having the Anytime Sprinkle with yogurt, or blending the Strawberry Banana Smoothie Mix into yogurt, kefir or a calcium enriched plant milk, you’re not only helping your heart, you’re also helping your bones.