Calcium is a nutrient commonly known for the important role it plays in maintaining strong bones and teeth. It is found in various food sources, such as dairy products like milk, cheese, and yoghurt, as well as dark green leafy vegetables, canned sardines, and certain fruits. The recommended daily intake of calcium for adults below the age of 50 is 1000mg, or 1g. As adults age and their bones become weaker, it is recommended to increase calcium intake to an average of 1000mg to 1200mg per day.
Not only does calcium play a crucial role in strengthening bones and teeth, but it also circulates through the bloodstream to ensure the proper functioning of other bodily processes. It plays an adjunctive role in regulating blood pressure, muscle contractions, and heart rhythm.
Bone Function and Metabolism
Bone plays an integral role in enabling humans to be mobile while also serving as a form of protection and a storage space for certain minerals, such as calcium. During childhood, bones undergo a process called modelling, during which they grow and move into their spaces.
As one ages and reaches adulthood, the bones undergo a remodelling process throughout life. For bones to remodel, a specific process is required. This process involves both the building and breaking down of bones, resulting in healthy and strong bones over the years. When bones undergo this process, it is often referred to as bone metabolism. There are four types of bone cells that play a role in ensuring optimal bone remodelling:
- Osteoblasts: These cells are responsible for bone formation, which builds new bone tissue.
- Osteoclasts: These cells break down bone during the resorption process.
- Osteocytes: These cells are sensitive to any strain on the bones and hormonal changes, thus regulating the bone remodelling process.
- Bone lining cells: Present on the surface of bone tissue when the bones are not undergoing remodelling, these cells act as a shield against osteoclasts and can later be stimulated to form osteoblasts and build new bone.
Regulation of Calcium Levels
Most of the calcium in the body is stored in the bones, while calcium levels throughout the body are controlled via the parathyroid gland, which is situated behind the thyroid gland. This gland produces parathyroid hormones responsible for regulating calcium levels in the body. These hormones control calcium levels by determining the rate at which calcium is released from its stores in the bones to the bloodstream and also the amount of calcium reabsorbed via the kidneys. The latter factor plays an important role in regulating blood pressure.
Another hormone released by the thyroid gland, known as calcitonin, typically reduces calcium levels in the body when these levels rise above normal. Calcitonin inhibits the activity of osteoclasts and decreases calcium in the bloodstream by inhibiting the release of calcium during bone breakdown. It also reduces the reabsorption of calcium from the kidneys, resulting in lower calcium levels circulating in the bloodstream. An element that plays an interesting symbiotic role alongside calcium is vitamin D. The levels of vitamin D in the body determine the small intestine’s ability to absorb calcium.
When vitamin D levels are low, calcium absorption decreases, and the excess calcium is excreted. Calcium levels are also regulated via the excretion of excess calcium, which can occur through urine, faecal matter, and sweat. Calcium excreted in the urine is usually regulated by the kidneys, where calcium that is not reabsorbed into the bloodstream is excreted. Calcium excreted in faecal matter occurs when the remaining calcium that is not absorbed by the small intestine is eliminated.
Conditions Related to Bone Metabolism and Calcium
One of the most common bone metabolism disorders is osteoporosis. Osteoporosis usually occurs in older age and is more prevalent in women than in men. Most of the time, it is due to the post-menopausal drop in oestrogen, which leads to a higher rate of bone resorption and a lower rate of bone formation. This results in weaker bones and lower bone density, ultimately leading to fractures, especially in the hips and forearms.
Another condition that can occur more frequently in older patients is osteomalacia. This condition arises when there is a reduction of minerals within the bone matrix and usually presents with signs such as muscle weakness, bone pain, and fractures. In some cases, the bones fail to mineralise calcium, even when calcium levels in the bloodstream are adequate. It is important for healthcare professionals to encourage the elderly to consume sufficient calcium through food or supplements, along with vitamin D, to ensure optimal absorption and prevent the degradation of bone quality.
