Preventing osteoporosis: which blood values (vitamin D, calcium) to test

Preventing osteoporosis starts with knowing where you stand, not with a pill. Here's the catch: you can't see your bone density in your blood, but you can see your vitamin D status. Across Europe, an estimated 13 percent of people had a vitamin D level below 30 nmol/l (PMID 26864360).

Doctors sometimes call osteoporosis a "silent disease". You usually feel nothing, until a bone breaks.

What strikes me about most pages on this: they shout "eat more calcium" and stop there. They forget to say that your bones themselves barely show up in blood, while your vitamin D very much does.

What is osteoporosis exactly?

Osteoporosis means your bones become more porous and brittle. Bone mass drops and the internal structure weakens, so a bone breaks more easily. You build most of your bone mass around age 30, and it slowly declines after that. In women it often speeds up after menopause.

Your skeleton is living tissue. It is broken down and rebuilt your whole life, every single day.

Until roughly age 30 the building wins. After that the balance slowly tips towards breakdown.

In women this accelerates around menopause, as oestrogen production falls. Oestrogen slows bone breakdown, so when it drops away, you often lose bone mass faster.

The numbers show how big this is. In the EU an estimated 22 million women and 5.5 million men had osteoporosis, with around 3.5 million new fractures in a single year (PMID 24113837).

A fracture after a minor fall is often the moment people first hear about their osteoporosis. You would rather get ahead of that. For more on what changes from your forties on, read which blood values to monitor as you age.

Can you see osteoporosis in a blood test?

No, not directly. There is no blood value that proves osteoporosis. The diagnosis is made with a DEXA scan, which measures your bone density. Blood work does something else: it gives context, such as your vitamin D and calcium status, factors that play into how your bones hold up.

That distinction matters more than it sounds. You measure bone density with an X-ray, not with a tube of blood.

A DEXA scan compares your bone density against that of a healthy young adult, the so-called T-score. At a T-score of -2.5 or lower, doctors speak of osteoporosis.

Blood does not show that score. What it can show is whether your building blocks are in order.

Compare it to a house. The DEXA scan looks at the walls themselves, the blood test at whether there are enough bricks and cement in stock.

So a tidy blood result is reassuring, but no proof that your bones are strong. And a low vitamin D does not mean osteoporosis, only that one building block sits on the low side.

Which blood values relate to your bone health?

For your bones, doctors mainly look at three values: vitamin D (25-OH), calcium and sometimes PTH (parathyroid hormone). Vitamin D helps your body absorb calcium. Calcium is the primary building block of bone. PTH regulates your calcium balance and can be raised when something is out of kilter.

Vitamin D is the value you hear about most. You measure it as 25-OH vitamin D in nmol/l, and it reflects your stores over the past weeks. The marker itself is explained on vitamin D (25-OH).

Calcium in your blood is peculiar: your body keeps it tightly regulated. Even with osteoporosis, calcium in the blood often stays plainly normal, because your body will pull it from your bones if needed.

That is exactly why PTH can add context. A raised PTH alongside a low-normal calcium can suggest your body is working to keep the calcium level up.

Preventing osteoporosis: what can you do yourself?

Preventing osteoporosis usually comes down to three things: getting enough calcium, enough vitamin D, and loading your bones with movement. Adults need around 1000 mg of calcium a day. Strength training and weight-bearing movement can prompt your bones to stay strong. Discuss what suits you with your GP.

Calcium mostly comes from food. The Voedingscentrum names dairy, green vegetables and nuts as well-known sources.

Vitamin D is trickier, because your skin makes it mainly under sunlight. The Gezondheidsraad therefore advises certain groups, such as people over 70 and those who rarely go outside, to consider extra vitamin D. Whether that applies to you is something to discuss with your GP.

In a meta-analysis, calcium with vitamin D gave a 15 percent lower risk of fractures overall, and a 30 percent lower risk of hip fractures (PMID 26510847). Note: that is an average across large groups, not a promise for one person.

Movement is the third pillar, and easy to forget. Your bones grow stronger from loading, so walking, stairs and strength training all count. Why muscle strength and bone strength travel together sits in staying strong with age: muscle mass, strength training and the blood values involved.

Wondering whether a deficiency plays into your symptoms? Which values you can then have checked sits in vitamin deficiency: recognising symptoms and which vitamins to test.

When should you discuss bone health with your GP?

Discuss it with your GP if you break a bone after a light fall, if osteoporosis runs in your family, or if you get noticeably shorter, say more than 4 cm. An early menopause or long-term use of certain medicines can also be a reason. Your GP can assess whether a DEXA scan makes sense.

A fracture from a standing-height fall is a signal your GP takes seriously. Healthy bones usually do not break from that.

Height loss sounds harmless, but can point to collapsed vertebrae. If you measure a few centimetres shorter than before, mention it.

A blood result is a starting point here, not an end point. Take it along, place it next to your story, and let the doctor weigh what is needed.

Where do you start?

Start small: map out whether your vitamin D and calcium status are in order, and check whether you move enough. Those two blood values are measurable and give context, even though they do not prove your bone density. A DEXA scan is something you discuss with your GP if there is reason for it.

If you want to start from a measured baseline, you can have vitamin D and calcium included in a broader blood test. Take a look at the extended health checkup, for example.

Feeling mostly tired or flat rather than worried about your bones? Then staying vital with age: energy, sleep and the blood values you can check fits better.

My advice stays plain. Measure what you can measure, be honest about what blood does not show, and leave the big decisions to your GP.

References

1. Weaver CM, Alexander DD, Boushey CJ, et al. Calcium plus vitamin D supplementation and risk of fractures: an updated meta-analysis from the National Osteoporosis Foundation. Osteoporos Int. 2016;27(1):367-376. PMID 26510847.
2. Cashman KD, Dowling KG, Škrabáková Z, et al. Vitamin D deficiency in Europe: pandemic? Am J Clin Nutr. 2016;103(4):1033-1044. PMID 26864360.
3. Hernlund E, Svedbom A, Ivergård M, et al. Osteoporosis in the European Union: medical management, epidemiology and economic burden. Arch Osteoporos. 2013;8(1):136. PMID 24113837.
4. Gezondheidsraad and Voedingscentrum. Public information on vitamin D, calcium and bone health. Available via gezondheidsraad.nl and voedingscentrum.nl.

Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss treatment decisions with your GP.