March 29, 2026 Health Topics

Bone Health: Calcium, Vitamin D, and Related Biomarkers

Q: What blood tests are used to assess bone health?

The most commonly ordered blood tests for bone health include serum calcium (total and ionised), 25-hydroxyvitamin D (25-OH vitamin D), serum magnesium, alkaline phosphatase (ALP), and parathyroid hormone (PTH). In some cases, vitamin K status and bone-specific markers such as osteocalcin or C-telopeptide (CTX) may also be measured. These tests assess nutrient availability and bone turnover rather than bone density directly—a DEXA scan is required to measure bone mineral density.

Q: What is the optimal vitamin D level for bone health?

The Endocrine Society defines vitamin D sufficiency as a serum 25-OH vitamin D level of 30 ng/mL (75 nmol/L) or higher. Levels between 20 and 29 ng/mL are considered insufficient, and levels below 20 ng/mL are classified as deficient. Some experts in bone health advocate for levels of 40–60 ng/mL for optimal bone protection, particularly in older adults at risk for osteoporosis, though supplementation decisions should be made with a healthcare provider.

Q: How does vitamin K relate to calcium and bone health?

Vitamin K—particularly vitamin K2 (menaquinone)—activates osteocalcin, a protein made by bone-forming cells that is essential for binding calcium into the bone matrix. Without sufficient vitamin K2, calcium may be deposited in soft tissues such as arteries rather than incorporated into bone. This is why calcium, vitamin D, magnesium, and vitamin K are often considered together as a nutritional cluster for bone health. Blood tests for vitamin K status are not always routinely ordered but can be assessed through functional markers such as undercarboxylated osteocalcin.

Bone is living tissue that is constantly being broken down and rebuilt. The blood biomarkers that reflect calcium metabolism, vitamin D status, and mineral balance give clinicians—and you—a measurable window into skeletal health long before symptoms appear.

Why Blood Tests Matter for Bone Health

Osteoporosis and low bone density are largely silent conditions—most people do not know their bones are weakening until a fracture occurs. While a DEXA scan directly measures bone mineral density, routine blood tests can reveal nutritional deficiencies and metabolic imbalances that drive bone loss years before a scan would show concern. Identifying and correcting these imbalances early is one of the most effective strategies for preserving skeletal strength throughout life.

Key Bone Health Biomarkers

Serum Calcium

Calcium is the most abundant mineral in the body, with approximately 99% stored in bones and teeth. The 1% circulating in blood is tightly regulated by parathyroid hormone (PTH) and vitamin D. A normal total serum calcium range is 8.5–10.2 mg/dL (2.12–2.55 mmol/L). Hypocalcaemia (low calcium) can signal vitamin D deficiency, hypoparathyroidism, or malabsorption, whereas hypercalcaemia (high calcium) may indicate primary hyperparathyroidism or, less commonly, malignancy. Explore the Calcium biomarker page for full reference ranges.

25-Hydroxyvitamin D (25-OH Vitamin D)

Vitamin D is essential for intestinal calcium absorption. Without adequate vitamin D, the body can only absorb 10–15% of dietary calcium, compared with 30–40% when vitamin D status is sufficient.[1] The 25-OH vitamin D test is the best clinical measure of overall vitamin D status. The Endocrine Society defines sufficiency as 30 ng/mL (75 nmol/L) or higher, insufficiency as 20–29 ng/mL, and deficiency as below 20 ng/mL.[2] Vitamin D deficiency is estimated to affect more than one billion people globally.[1] See the Vitamin D (25-OH) biomarker page for detailed interpretation.

Magnesium

Approximately 60% of the body's magnesium is stored in bone, where it contributes to the structural integrity of the hydroxyapatite crystal lattice.[3] Magnesium also regulates PTH secretion and activates vitamin D.[3] Low serum magnesium impairs PTH release and reduces the conversion of vitamin D to its active form, creating a compounding effect on calcium absorption and bone mineralisation. Learn more on the Magnesium biomarker page.

Vitamin K

Vitamin K—particularly the K2 form (menaquinone)—activates osteocalcin, the protein produced by osteoblasts that anchors calcium into the bone matrix. Inadequate vitamin K2 results in undercarboxylated osteocalcin, which cannot bind calcium effectively. Several prospective studies have linked higher vitamin K intake and better vitamin K status with reduced fracture risk and better bone mineral density. [4] Visit the Vitamin K biomarker page to understand how this marker is measured and interpreted.

Bone Health Biomarker Reference Table

Biomarker	Normal / Optimal Range	Concern Threshold	Clinical Significance
Serum Calcium	8.5–10.2 mg/dL	< 8.5 or > 10.2 mg/dL	Bone mineralisation, muscle function
25-OH Vitamin D	≥ 30 ng/mL	< 20 ng/mL (deficient)	Calcium absorption, bone density
Serum Magnesium	1.7–2.2 mg/dL	< 1.7 mg/dL	PTH regulation, vitamin D activation
Vitamin K	0.2–3.2 ng/mL (K1)	< 0.2 ng/mL	Osteocalcin carboxylation, calcium binding
Alkaline Phosphatase (ALP)	44–147 IU/L (adults)	Elevated: high bone turnover	Bone formation activity

Lifestyle and Nutritional Support for Bone Health

Weight-bearing exercise—including walking, jogging, and resistance training—stimulates osteoblast activity and helps maintain bone mineral density throughout life. Nutritional adequacy across the calcium-vitamin D-magnesium-vitamin K cluster is equally important: these nutrients work synergistically, and deficiency in one can blunt the effectiveness of the others.[5] Adequate protein intake also supports the collagen matrix of bone, and avoiding smoking and excessive alcohol consumption are independently associated with lower fracture risk. Tracking these blood markers over time helps you and your healthcare provider identify and address deficiencies proactively.

Key Takeaway: Bone health depends on a cluster of interacting nutrients—calcium, vitamin D, magnesium, and vitamin K—all of which can be assessed through blood tests. Monitoring these markers regularly with the Health3 app gives you a longitudinal view of your skeletal health and flags deficiencies early.

Frequently Asked Questions

What blood tests are used to assess bone health?

The most commonly ordered blood tests for bone health include serum calcium (total and ionised), 25-hydroxyvitamin D (25-OH vitamin D), serum magnesium, alkaline phosphatase (ALP), and parathyroid hormone (PTH). In some cases, vitamin K status and bone-specific markers such as osteocalcin or C-telopeptide (CTX) may also be measured. These tests assess nutrient availability and bone turnover rather than bone density directly—a DEXA scan is required to measure bone mineral density.

What is the optimal vitamin D level for bone health?

The Endocrine Society defines vitamin D sufficiency as a serum 25-OH vitamin D level of 30 ng/mL (75 nmol/L) or higher. Levels between 20 and 29 ng/mL are considered insufficient, and levels below 20 ng/mL are classified as deficient. Some experts in bone health advocate for levels of 40–60 ng/mL for optimal bone protection, particularly in older adults at risk for osteoporosis, though supplementation decisions should be made with a healthcare provider.

How does vitamin K relate to calcium and bone health?

Vitamin K—particularly vitamin K2 (menaquinone)—activates osteocalcin, a protein made by bone-forming cells that is essential for binding calcium into the bone matrix. Without sufficient vitamin K2, calcium may be deposited in soft tissues such as arteries rather than incorporated into bone. This is why calcium, vitamin D, magnesium, and vitamin K are often considered together as a nutritional cluster for bone health. Blood tests for vitamin K status are not always routinely ordered but can be assessed through functional markers such as undercarboxylated osteocalcin.

Monitor Your Bone Health Markers With Health3

Scan your lab results, track vitamin D trends, and explore how calcium, magnesium, and vitamin K interact—all in one place.

References

Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266-281. PubMed
Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930. PubMed
Rude RK, Singer FR, Gruber HE. Skeletal and hormonal effects of magnesium deficiency. J Am Coll Nutr. 2009;28(2):131-141. PubMed
Cockayne S, Adamson J, Lanham-New S, et al. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med. 2006;166(12):1256-1261. PubMed
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. PubMed

Medical Disclaimer: This page is for informational and educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making changes to your health regimen. Read our full Content Standards & Medical Disclaimer.