Calcium is the most abundant mineral in the human body and it helps in the development of strong bones and teeth. 
Approximately 99% of the calcium is stored in bones and teeth, while 1% is found in blood, muscle, and other tissues.  Calcium is used to provide bone strength, it helps build and maintain strong bones. On the other hand, our bodies also need calcium to circulate blood, move muscles, and release hormones. Hence, it’s important to get enough calcium from the food we eat as our bodies do not produce calcium on its own.
Do you know it’s useless to consume food that provides calcium if your body couldn’t absorb or retain them? In order to have sufficient calcium for your health, you must first know how your body absorbs and retain them after consumption.
Why do we need Magnesium?
Magnesium is an essential mineral that plays several important roles in bodily function such as maintaining healthy bones, supporting muscle, energy production and regulate nerve function. 
Our bodies need vitamin D to absorb calcium. Vitamin D is an important nutrient in your body to keep bones strong and healthy by promoting the absorption of calcium. However, the Vitamin D that we consumed orally or made in the skin from sun exposure is considered biologically inactive, it must be activated by a two-step process within the kidney and liver enzymes. Both of these enzymes need magnesium in order to function properly.
Magnesium helps to convert Vitamin D into its active form  which aids in calcium absorption. Without enough magnesium, calcium may not be fully utilized and absorbed by the body.  This may become toxic, causing some health problems such as kidney stones, kidney failure, heart function problems, constipation as well as confusion and cognitive problems. 
How much Calcium and Magnesium do we need per day?
The recommended amount of calcium is at least 1000 mg per day for adults. Women over the age of 51 and men over the age of 70 are advised to increase their daily intake to 1,200mg.
For Magnesium, the recommended amount is 300mg to 500mg per day.
However, the absorption of dietary calcium can be affected by age.  For infants and children, the absorption of dietary calcium is about 60%, but it decreases to about 25% for adults and continues to decline with age. That’s why it’s important to consume enough Magnesium to ensure calcium has been absorbed and retained in our bodies.
Since both magnesium and calcium are work closely, it is important to take the correct amount of both magnesium and Calcium in order for them to be effective.
A good rule of thumb often used is the 2:1 calcium-to-magnesium ratio. For instance, if you take 1000mg of calcium, you should also take 500mg of magnesium.
How to increase intake of magnesium
It's always the best to get all the magnesium that you need from natural source. Magnesium can be easily found in the food supply in both plant and animal foods.
The foods that are high in magnesium include:
- Whole grains
- Dark leafy green
- Dark chocolate (containing at least 70% cocoa)
Calcium and magnesium are two macro-minerals that are vital in maintaining strong and healthy bones. It is important to maintain adequate magnesium levels when taking calcium in order for them to be effective. Whether you are getting these minerals through diet or supplementation, the correct balanced levels of calcium and magnesium will promote absorption and retention of calcium.
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2. Harvard T.H. Chan (School fo Public Health). Calcium. [https://www.hsph.harvard.edu/nutritionsource/calcium/]
3. National Institutes of Health. Magnesium. 2021. [https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/]
4. Nutritional Magnesium Association. Without Magnesium, Vitamin D is Ineffective – Dr. Mercola. [http://www.nutritionalmagnesium.org/without-magnesium-vitamin-d-supplementation-is-ineffective-dr-mercola/]
5. Oregon State University. Magnesium. [https://lpi.oregonstate.edu/mic/minerals/magnesium]
6. Cleveland Clinic. Are You Taking Too Many Calcium Supplements?: How to get enough but avoid hypercalcemia. 2019 [https://health.clevelandclinic.org/are-you-taking-too-many-calcium-supplements/]