Testing for Deficiency · why blood numbers aren't your stores

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Connected to · 2

cofactor · 1

Multivitamin
Testing should start with a question and then choose the test, not run a batch of tests and go looking for problems. Apply the same approach to supplements and the question becomes: does taking this actually do anything?

regulates · 1

Osteoporosis
Blood calcium is held tightly at about 2.2–2.6 mmol/L by a negative-feedback loop: when intake is low, parathyroid hormone draws calcium out of bone to make up the difference. So an abnormal blood calcium says nothing about whether you eat enough; it means the control system itself has gone wrong (the parathyroid glands, the kidneys or certain tumors), which needs a doctor. How your bones are doing is judged by bone density.

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Normal blood calcium says little

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When the calcium line on your health-check report reads normal, it tells you almost nothing about whether your bones have enough calcium.

Calcium in the blood is not a window into the warehouse; it is a pool held under guard. In your neck are four rice-grain-sized glands, the parathyroid glands, that constantly taste the blood. The moment blood calcium starts to fall, they release a hormone that brings it back up, parathyroid hormone (). In bone, this hormone wakes up the cells whose job is to break bone down and pulls calcium out of bone into the blood; in the kidneys, it makes them let a little less calcium leak away (Peacock 2010).

So blood calcium is locked into a very narrow band. The body would rather take its own skeleton apart than let that number drift.

What that means for you: a person can have their bones slowly hollowed out while blood calcium stays normal the whole time. The US National Institutes of Health's calcium fact sheet says it plainly: blood calcium does not reflect nutritional status, because it is regulated so tightly (NIH ODS). More than 99% of the body's calcium is in bones and teeth; the little in the blood was never there to show you the stores.

Keep this picture: a guarded pool, not a window. The later chapters of this story are all variations on it.

Educational content, not medical advice — consult a clinician.

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Testing for Deficiency · why blood numbers aren't your stores

Story

Connected to · 2

cofactor · 1

Multivitamin
Testing should start with a question and then choose the test, not run a batch of tests and go looking for problems. Apply the same approach to supplements and the question becomes: does taking this actually do anything?

regulates · 1

Osteoporosis
Blood calcium is held tightly at about 2.2–2.6 mmol/L by a negative-feedback loop: when intake is low, parathyroid hormone draws calcium out of bone to make up the difference. So an abnormal blood calcium says nothing about whether you eat enough; it means the control system itself has gone wrong (the parathyroid glands, the kidneys or certain tumors), which needs a doctor. How your bones are doing is judged by bone density.

Read full story

Stop 1/7

Normal blood calcium says little

EVIDENCEGUIDE 1 · REVIEW 1

READ THE ORIGINAL

When the calcium line on your health-check report reads normal, it tells you almost nothing about whether your bones have enough calcium.

Calcium in the blood is not a window into the warehouse; it is a pool held under guard. In your neck are four rice-grain-sized glands, the parathyroid glands, that constantly taste the blood. The moment blood calcium starts to fall, they release a hormone that brings it back up, parathyroid hormone (). In bone, this hormone wakes up the cells whose job is to break bone down and pulls calcium out of bone into the blood; in the kidneys, it makes them let a little less calcium leak away (Peacock 2010).

So blood calcium is locked into a very narrow band. The body would rather take its own skeleton apart than let that number drift.

What that means for you: a person can have their bones slowly hollowed out while blood calcium stays normal the whole time. The US National Institutes of Health's calcium fact sheet says it plainly: blood calcium does not reflect nutritional status, because it is regulated so tightly (NIH ODS). More than 99% of the body's calcium is in bones and teeth; the little in the blood was never there to show you the stores.

Keep this picture: a guarded pool, not a window. The later chapters of this story are all variations on it.

Educational content, not medical advice — consult a clinician.