Trait overview: Blood calcium level

Monday, May 04, 2020. Author FitnessGenes

Trait overview: Blood calcium level

While we often think of calcium as being particularly important for healthy bones and teeth, this mineral is also essential for heart function, muscle contraction and nerve signalling.

Calcium is both a micronutrient and macromineral:

  •   Micronutrient: we require only small quantities of calcium relative to macronutrients (fat, carbohydrates and protein).
  •   Macromineral: it is needed in larger amounts than so-called ‘trace minerals’, such as copper and magnesium.

Many of calcium’s functions in the body stem from the fact that it forms an ion: an electrically charged atom.

The movement of calcium ions into and out of cells causes differences in electrical charge and voltage across cell membranes.

This principle is central to heart contraction, skeletal and smooth muscle contraction, and nerve signalling.


Where is calcium stored in the body?

There are three main areas where our body stores calcium:

  1. Bones - mainly in bone mineral as part of a crystalline compound called hydroxyapatite.
  1. Blood and extracellular fluid (ECF) - predominantly in plasma (or serum) and the fluid that surrounds cells.
  1. Intracellular calcium - cells store calcium in various internal organelles, including the mitochondria.


Why do blood calcium levels need to be regulated?

Cell function

In order for cells to use calcium for internal biochemical and signalling processes, they must be kept topped up with calcium ions supplied by the blood.


Nerve and muscle function

As calcium ions carry an electrical charge, maintaining a constant level of calcium both inside and outside of cells stabilises the voltage across cell membranes. This is important for healthy nerve, muscle and heart function. 

On a related note, calcium ions regulate the opening and closing of special channels called voltage-gated ion channels. These allow other ions such as sodium, potassium and chloride to enter nerve and muscle cells, which affects their electrical excitability. This has an effect on transmission of nerve signals and muscle contraction. 

If calcium levels in the blood are too low, these voltage-gated channels are more likely to be open, making nerves and muscle cells more overly excitable. In some cases, this can lead to muscle spasms.

Conversely, if calcium levels in the blood are too high, voltage-gated channels are more likely to remain closed, making nerves and muscle less excitable. 


Blood clotting

If you’ve ever cut yourself shaving, you’ll notice that the bleeding soon stops. This is due to the formation of blood clots, which are made from a molecule called fibrin.

Calcium is essential for the formation of fibrin and various other stages in blood clotting. Low levels of calcium in the blood can therefore delay blood clotting.

How are blood calcium levels regulated?

Calcium levels in the blood are kept within a strict range by constantly adjusting the rate at which calcium is absorbed, excreted, and converted into bone mineral.

The three main organs that regulate blood calcium levels are:

  1. Small intestine – which absorbs calcium from food, a process stimulated and enhanced by Vitamin D.

  2. Kidneys – which reabsorb or release calcium into the urine, depending on the body’s demands.

  3. Bones – which can be remodelled (broken down or built up) to increase or decrease blood calcium levels.


What happens when blood calcium levels fall too low?

Levels of blood calcium are monitored by a special calcium-sensing receptor (CaSR), located in the parathyroid gland, thyroid and kidneys.

When calcium levels fall, less calcium binds to the CaSR, triggering the increased production of a hormone called  parathyroid hormone (PTH).

PTH then increases calcium levels in the blood by stimulating:

  • the production of Vitamin D to increase calcium absorption by the small intestine

  • reabsorption of calcium by the kidneys. 

  • breakdown of bone tissue (resorption) to release calcium into the bloodstream. 

What happens when blood calcium levels become too high?

When calcium levels rise, more of it binds to the CaSR receptor. This suppresses the release of PTH and instead, causes your thyroid gland to releases a hormone called calcitonin.

Calcitonin helps to reduce blood calcium levels by:

  • inhibiting the breakdown of bone tissue.

  • inhibiting the reabsorption of calcium by the kidneys so more is filtered out in urine.


The Blood Calcium Level trait

The FitnessGenes blood calcium level trait combines a number of genetic factors that influence calcium metabolism to predict whether members are at risk of high blood calcium levels. It also accounts for your age. 

Depending on the genetic variants that they carry, FitnessGenes members are placed into one of six individual trait bands:

1) low, 2) medium and 3) high risk of high blood calcium (young)

4) low, 5) medium and 6) high risk of high blood calcium (old)

One of the genes that we analyse includes the CASR gene, which encodes the CaSR protein. Variants of this gene affect how well your parathyroid glands and kidneys respond to changes in serum calcium levels. They therefore partly influence your risk of low or high blood calcium levels.

For those at risk of high blood calcium levels, limiting dietary intake of calcium to 1200mg per day as well as monitoring Vitamin D levels is important. Supplementing with magnesium at night can also help with general muscle relaxation and reduce PTH secretion.


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