By Stacey Penney, MS, NASM-CPT, CES, PES, FNS

We all know that calcium is essential for strong bones and teeth, but what else does it do? How about its critical roles in muscle contractions, nerve impulses, blood clotting, and cellular metabolism? Recent research has even highlighted its role in weight management, controlling cholesterol and hypertension, along with reducing the risks of certain cancers. Find out more of what calcium does, the recommended dietary intake, and the sources to get it from.

What Calcium Does

Skeletal Strength

Bones and teeth are where 99% of the body’s calcium can be found (1,2). Bones are continually remodeling, whether being broken down and going through resorption or being reformed with deposits of calcium (1-3). Bone growth and density increases the most during childhood and adolescences when more bone is deposited than removed (1,2). The bones also serve as the body’s calcium reservoir. Most people have reached their bone mass peak by age 30, after that there is slightly more bone lost than gained during the remodeling process (1,2).

Osteoporosis is when there is a decrease in bone mass and density, and the bones become porous and fragile (1-3). This has a higher incidence in post menopausal women when estrogen and progesterone production declines, but can also be caused by low calcium and vitamin D intake, eating disorders, smoking, too much alcohol, and a lack of physical activity (or bed-rest) (1,3,4). Developing and maintaining peak bone mass is key in preventing osteoporosis. Active women athletes should also be concerned with the female athlete triad, a syndrome of disordered eating, amenorrhea (loss of normal menstrual cycle), and osteoporosis (1,2,5). This syndrome can happen when female athletes increase their training, and/or decrease their energy and calcium intake, leading to an increased risk of bone fractures (1,5).

Nerve and Muscle Function

Calcium’s positive molecule is important to the transmission of nerve impulses to the muscle fiber via its neurotransmitter triggering release at the junction between the nerves (2,6). Inside the muscle, calcium facilitates the interaction between actin and myosin during contractions (2,6). Recall the protein structures of tropomyosin and troponin, both located on the actin filament. Calcium binds to the troponin, causing a position change in tropomyosin, exposing the actin sites that myosin will attach to for a muscle contraction (5,6).

Blood Clotting

Without calcium blood would not clot. Calcium needs to be present in the blood for the formation of fibrin, an insoluble protein that forms a fibrous network for the blood clot’s framework (2).

And a few more…

Calcium also plays an important role in blood pressure regulation, heart rhythm, cellular metabolism, water balance and immune function, along with energy and fat metabolism (1,2,5).

How Much Calcium?

Many people don’t get the recommend daily amounts of calcium, especially women (7). Below is an overview of the daily calcium needs for adolescents and adults.

Though it’s easy enough to see how much calcium is needed on a daily basis, it can be a challenge to track just how much you are actually getting (or losing) because calcium absorption is very inefficient (1,2). Generally, we only absorb between 25% and 35% of the calcium we consume. Calcium absorption can vary due to age (highest during pregnancy and infancy, lowest in old age), presence of vitamin D (increases absorption in the intestine), hormonal status (drop in estrogen for women, low testosterone for men lowers absorption), the body’s need for calcium, and overall calcium intake (inversely related, the more you eat the less you absorb) (1-3).

Foods high in calcium include dairy products, green leafy vegetables, canned fish with bones (sardines, salmon), some tofu products, and calcium-fortified products (1,2,8). Milk is often touted as one of the best sources of calcium, but there are plenty of other non-animal sources- you just may need to eat quite a few servings to get the same amount of bio-available calcium (2,8)! Though high in calcium content, some foods, such as spinach, are poorly absorbed by the body because of the oxalates that are bound to the calcium (2,8).

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