Magnesium, Calcium and the Stress Response

When you read about magnesium you will often find that the balance of magnesium and calcium is referred to. This article aims to explain how magnesium is used in the body and the nature of its relationship with calcium.

The Basic Roles of Magnesium and Calcium

The calcium ion (Ca2+) is remarkably similar to that of magnesium (Mg2+) and yet they act very differently. They work together but antagonistically to help maintain normal function in the body.

Calcium works to excite nerves, to stimulate a reaction, thus allowing the body to communicate, contract muscles etc. Magnesium however is vital for inhibitory control, blocking certain channels to prevent unwanted reactions, allowing muscles to relax and generally helping to control the nervous system. It is especially important for control of the cardiovascular system and regulation of the heart, preventing misfired signals caused by excess calcium, to maintain a steady even beat with a strong contraction.

Both elements also have a number of other roles in the body and are vital for a huge range of interrelated functions which contribute to overall health, energy metabolism, brain function and so forth.

Compelling research is finally gaining magnesium the recognition it deserves. For instance, it would be hard to find someone that did not know that calcium is good for bone structure, however very few people are aware that magnesium is also hugely important, and that treatments for osteoporosis and similar conditions require a combination of magnesium and calcium.

Absorption Characteristics of Magnesium and Calcium

The body is extremely well equipped to control the movement of calcium; it is able to actively pump calcium to where it is needed and to store plentiful amounts. Humans are able to control how much is absorbed during digestion, horses are thought to be slightly different in that they absorb large amounts of calcium during digestion and then rely on urinary excretion to remove the excess.

Magnesium must also be controlled through facilitated absorption because cell membranes are naturally impermeable to the Mg2+ ion, however it is not controlled in such a vigorous manner, and is dependant on the availability of open channels in the membranes designed for the passage of it and similar ions. This is reflective of the balancing, regulatory role of magnesium in the body.

This is an important concept when considering your horse’s ability to utilise dietary components. Calcium is very freely available and the horses is continually having to excrete excesses to ensure normal levels in the tissue.

Magnesium however is very difficult for the horse to absorb, the more passive nature of absorption means that the body cannot make up a shortfall by increasing absorption; it is dependant on a constant plentiful supply.

Magnesium absorption is also greatly hindered by the presence of competitive ions, namely calcium and potassium. What this means is that the more calcium you feed, the less magnesium will be absorbed, thus exacerbating any imbalance. In stark contrast to this however, increasing dietary magnesium actually helps the body to absorb and utilise calcium. So more calcium means less magnesium, but more magnesium means more calcium too!

Furthermore, the horse stores calcium in bone. During times of dietary shortage it can take calcium from bone stores in order to maintain required levels within other tissues. This is a normal and healthy function for the bone, and is only detrimental when calcium cannot be replenished, thus gradually stripping the bone of calcium and weakening its structure. This is why calcium deficiency manifests itself as skeletal problems developed over time, rather than short term muscular or nervous issues; the body’s ability to store and redistribute calcium ensures that the nerves and other cells always have a plentiful supply.

The Modern Equine Diet

Horses have evolved grazing a large amount of very rough pasture. Unfortunately this diet simply cannot sustain a horse which is required to work, we need to greatly increase calorie and nutrient intake so that we can get the results that we demand. We have also taken away the horses ability to roam.

Changing the horse’s diet so dramatically has inevitably caused problems from gut acidity, to tying-up, laminitis and behavioural issues. We are now starting to understand why all these problems exist; it is just a case of getting it right.

The biggest problem for calcium is the Ca:P (calcium : phosphorous) ratio. Straight grains are relatively high in phosphorous, which can hinder calcium absorption thereby causing the horse to become calcium deficient. This is a problem that has been addressed by modern hard feed, so it is not something you have to worry about unless you feed traditional straights. Oat balancers are primarily designed to address this issue.

Things are not so simple for magnesium. The large amounts of calcium and other ions in modern feed hinder the absorption of magnesium, so even increasing magnesium content has minimal effect. High fat diets will also greatly reduce magnesium absorption, but have no detrimental effect on calcium absorption. An additional problem is that processed feeds spend far less time being digested, allowing less time for absorption. So not only is magnesium being pushed out by other compounds, it has less time to compete.

Grazing can also vary greatly in magnesium content, very sandy or wet soil will be extremely low in magnesium and there will be less magnesium in grass through the winter. New grass (seen in the spring and again in autumn) is very high in calcium and low in magnesium thus often causing magnesium deficiency. This imbalance is a very common problem which can be lethal to ruminants and has to be carefully monitored by farmers. The equine digestive tract is more akin to our own, so luckily we do not see this extreme reaction, but the high level of calcium is a major cause of that spring grass ‘whizz’ we normally attribute solely to sugar content, and it is likely to be a significant factor with cases of laminitis.

Understanding the Stress Response

Exposure to stress triggers a whole chain of reactions, these are survival responses, mostly designed to equip us for ‘fight or flight’. But in our modern life, as is the case with the domesticated horse, we are exposed to a huge amount of continual stress factors and the fight or flight response is completely useless to us. And to a horse, that presumably cannot rationalise about what it is experiencing, this inability to respond effectively can be another stress trigger in itself.

Stress comes in many forms, from isolation, to a change in routine, a fright, pressure to work and concentrate, exercise, cold, noise, pain etc. Horses, like us, vary in how well they cope with various types of stress, and how they react. For some, the stress response is always partially engaged, leading to hypersensitivity. Nutrition can be a key factor for these individuals.

In response to stress, the body releases hormones and uses the nerves to increase heart, metabolic and breathing rates, redistribute blood flow away from the gut and bladder to the muscles, increase blood pressure, increase blood glucose and delay fatigue. Adrenaline is the most significant hormone in this reaction, and we will often refer to ‘the adrenaline kicking in’ when our horses get wound up.

Under normal conditions, the majority of calcium is kept outside of the cell, where as magnesium is mostly found inside the cell. Stress responses vitally involve the influx of calcium into the cells, thus dramatically altering the cell magnesium to calcium ratio. Calcium acts to encourage nerve excitation, adrenaline secretion and adrenaline response. The stress response subsides when magnesium is allowed to suppress all these factors so that they return to normal.

So, in the normal state cellular Mg:Ca ratio is high, i.e. lots of magnesium relative to calcium. But when dietary magnesium is low or there is an overwhelming amount of calcium, this balance can be disturbed causing a semi-stressed state, and often invoking a stress response from an inappropriate trigger. Because magnesium is important to reduce adrenaline levels and also reduce the cell’s response to adrenaline, low levels will mean that the stress response cannot subside as it should. This can also create a negative cycle, because a horse that is stressed requires greater levels of magnesium. Too little magnesium will cause a stress response, which furthers the need for magnesium of which there is a shortage.

Human Conditions (summary - for the full article click here)

When you understand the role of magnesium and calcium in the stress response, it starts to become clear why magnesium is such a key part in the treatment for a huge range of conditions.

Unsurprisingly depression, hypersensitivity, anxiety, behavioural disorders and panic attacks can all be symptoms of magnesium deficiency. Magnesium is also vital for proper melatonin and serotonin regulation, which greatly effect mood. It’s regulation of the nervous system mean that magnesium is routinely used for muscle issues such as cramping and restless leg syndrome, and is often beneficial for seizure disorders.

Magnesium is a key component of most heart disease treatments. Risk factors associated with heart disease such as high cholesterol, high blood pressure, and stress itself are all strongly associated with poor magnesium intake.

Inflammatory diseases, insulin resistance and gastric ulceration are further examples of health problems that can be linked to poor magnesium levels. The broad range of health effects is a good representation of just how fundamentally important magnesium is to us.


It is clear that we have altered our horse’s lifestyle in a way which is hugely detrimental to their health. In our country especially, the average horse owner is keen to try and give the best to their horse, but it is hard to sift through the huge amount of unregulated claims, grand statements and often misleading or under explained concepts.

Calcium is of vital importance to basic function and skeletal structure, so you should ensure an ample supply, especially in the growing horse. Fortunately the average equine diet does provide them with plentiful amounts, and providing that you are not feeding excessive amounts of phosphorous, calcium is very easily absorbed, utilised and stored by the horse. Modern feeding and the excessive stress demands of many horses however, can leave them very short of magnesium. This can impact both their health and their behaviour on many levels, and can impair their ability to use other nutrients, including calcium.

We demand a massive amount from our horses. Evidence repeatedly shows that magnesium supplementation is appropriate for any stress related problem, from poor concentration through to permanently stressed and overactive individuals

Magnesium Image
Calcium Image

You may also be interested in:

Magnesium and Laminitis

Gastric Ulcers

Rebecca Drane

Rebecca Drane, young Dressage Rider

Work and competition can be stressful for your horse, the resulting magensium depeletion can effect their performance and character in a way that is no fault of their own.