What bone density actually is

Bone density is the amount of mineral (mostly calcium and phosphorus) packed into a given volume of bone. Higher density means stronger bones; lower density means more fragility and higher fracture risk. After about age 30, everyone loses bone mass gradually. The question is whether you lose it fast enough to become a problem.

Conditions linked to low bone density

Osteoporosis is the big one: significant bone loss with fragile bones that can fracture from a simple fall.

Osteopenia is the warning shot before osteoporosis: lower-than-normal but not yet at the osteoporosis threshold.

Other contributors: hyperthyroidism, certain autoimmune diseases, chronic kidney disease, and long-term corticosteroid use.

Why Canadians should care

Roughly 1 in 3 women and 1 in 5 men over 50 will have an osteoporotic fracture. Osteoporosis Canada estimates more than 2 million Canadians have it, and that number's climbing as the population ages. Postmenopausal women and people with a family history are at the highest risk.

What blood tests show

Blood tests don't measure bone density directly. They measure the biochemistry behind it: minerals, hormones, and enzymes that drive bone metabolism. A few markers do most of the work.

• Calcium. The building block of bone. Low calcium can mean dietary issues or absorption problems. The body keeps blood calcium tight, though, so it can look "normal" even when bones are losing mineral.
• Vitamin D (25-hydroxyvitamin D). Required to absorb calcium. Low D is common in Canada, especially in winter. Below 30 ng/mL (75 nmol/L) is usually considered insufficient.
• Parathyroid hormone (PTH). Rises when blood calcium is low, pulling calcium out of bone to compensate. High PTH with low or borderline calcium and D is a red flag for ongoing bone loss.
• Alkaline phosphatase (ALP). A marker of bone turnover. Elevated ALP can point to conditions like Paget's disease, healing fractures, or other states of increased bone remodeling.

Looking at these together gives a picture of what's driving bone health. For example, low vitamin D plus high PTH usually means your body is robbing bone to keep blood calcium normal. Catching that early lets you fix it before density drops far enough to need treatment.

What abnormal results mean

A few common patterns:

• Low vitamin D plus low calcium plus high PTH. Classic pattern for bone loss driven by D deficiency. Common in Canadians, especially older adults.
• High alkaline phosphatase on its own (with normal liver tests) suggests increased bone turnover. Could be Paget's disease, healing fracture, or a metabolic bone condition.
• Normal calcium with high PTH can indicate primary hyperparathyroidism, which steadily depletes bone over time.

None of this diagnoses osteoporosis by itself, but it gives your clinician strong clues about whether bone is being lost and why.

How blood tests fit with DEXA scans

A DEXA (dual-energy X-ray absorptiometry) scan is the actual measurement of bone density. Blood tests tell you about metabolic factors; DEXA tells you the structural outcome. They work together: blood tests catch the causes early, DEXA confirms how far things have gone and tracks treatment.

If a blood panel turns up significant deficiencies or PTH abnormalities, a DEXA scan is usually the next step, especially if you're over 50 or have other risk factors.

Examples

1. Routine bloodwork picks up a problem early. A 68-year-old woman has routine bloodwork showing low vitamin D and borderline-low calcium. Her doctor orders a DEXA scan, which confirms osteopenia. She starts vitamin D and calcium supplementation along with weight-bearing exercise, and re-testing in two years shows stable density. Without that early bloodwork, she likely wouldn't have known until a fracture.
2. Unexplained fracture leads to diagnosis. A 72-year-old man has a wrist fracture from a minor fall. Bloodwork shows elevated PTH and alkaline phosphatase. DEXA confirms osteoporosis. He starts bisphosphonate therapy plus vitamin D and exercise, lowering his fracture risk significantly going forward.

DEXA scans and what they show

A DEXA scan is the standard test for measuring bone density. It uses two low-dose X-ray beams to estimate the mineral content of bone, usually at the hip and spine. It takes 10 to 30 minutes and the radiation dose is very low.

You get a T-score: a comparison to the bone density of a healthy 30-year-old of the same sex.

• T-score of -1.0 or higher: normal.
• Between -1.0 and -2.5: osteopenia.
• -2.5 or lower: osteoporosis.

The T-score guides treatment decisions and also helps track changes over time when you repeat the scan in a few years.

Blood tests vs. DEXA: when each one matters

Blood tests:

• Show metabolic causes early, before density drops.
• Cheap, available everywhere, and most are OHIP-covered.
• Don't measure density directly.

DEXA scans:

• Directly measure density.
• The standard for diagnosing osteoporosis and monitoring treatment.
• Need specialized equipment and a referral.

You generally want both: blood tests to find treatable causes, DEXA to measure the structural outcome.

If blood tests come back abnormal

1. Follow-up bloodwork to confirm and dig deeper (thyroid panel, kidney function, sex hormones, etc.).
2. DEXA scan if you're at risk or already over 50.
3. Treatment: vitamin D and calcium are the foundation. Bisphosphonates, denosumab, or other medications come in if density is low enough.
4. Lifestyle changes: weight-bearing exercise, quitting smoking, cutting back on alcohol, fall prevention at home.
5. Repeat testing at intervals depending on how aggressive the bone loss is.

In the next section, we will focus on prevention and management strategies to sustain and improve bone density, exploring actionable steps individuals can take to support their bone health across all life stages.

Keeping bones strong

Daily habits

1. Diet:
   • Calcium: 1,000 to 1,200 mg/day depending on age and sex. Dairy is easiest. Non-dairy sources include kale, almonds, sardines with bones, and fortified plant milks.
   • Vitamin D: 600 to 800 IU/day for most adults; many Canadians need more in winter. Sources include fortified milk, fatty fish, and supplements.
   • Protein: needed for bone matrix. Lean meat, fish, beans, dairy, and nuts.
2. Movement: weight-bearing exercise like walking, jogging, dancing, and resistance training. Aim for 150 minutes a week of moderate aerobic activity plus strength training twice a week. Balance work (yoga, tai chi) cuts fall risk.
3. Risk reduction: cap alcohol at recommended limits, quit smoking. Both directly weaken bone.
4. Screening: routine bone density screening starts at age 65 for women and 70 for men in Canada, earlier if you have risk factors (steroid use, family history, certain medications, low body weight).

Why routine screening matters

Bone loss is silent until it shows up as a fracture. Routine blood work and a baseline DEXA scan let you catch and treat low bone density before the first fracture, which is the goal.

Bottom line

Blood tests don't measure bone density, but they're the cheapest, earliest way to spot what causes it to drop: low vitamin D, calcium imbalance, parathyroid problems, and unusual bone turnover. Combined with a DEXA scan when needed, they give you a full picture of bone health early enough to act. If you're over 50 or have risk factors, ask your clinician about a baseline panel that includes calcium, vitamin D, and PTH.

Disclaimer: This blog post is intended for educational purposes only and should not be taken as medical advice. Always consult your healthcare provider for personal health concerns.