Calcium is the most abundant mineral in our body. 99% is stored in our bone and teeth and 1% in our blood. Other than bones, calcium is important for our vascular health, muscle function, nerve transmission and hormones.
Bone formation and Resorption
Our body is constantly remodeling our bones through formation and resorption (breakdown).
During our childhood and adolescence, our bone mineral density (BMD) increases as bone formation is greater than resorption.
In our 20s, our bone mass continues to grow and reaches peak bone mass (PBM) at around 30.
During middle age, BMD is stable as formation and resorption are roughly the same.
As we age further, our bone breaks down faster than formation, which can increase the risk of osteopenia (lower BMD), and osteoporosis (lower BMD with more fragile bones and higher risk of fracture).
Postmenopausal women are most at risk of osteopenia and osteoporosis due to lower level of oestrogen to protect their bones, but groups of other ages and gender can also be at risk.
Osteopenia and Osteoporosis
Osteopenia is somewhere between a healthy bone mineral density and osteoporosis. Our bones are densest at around age 30 and gradually deteriorate with ageing. Osteopenia usually occurs after 50, but does not always proceed to osteoporosis and can be improved with nutrition, exercise and medication.
Osteoporosis is defined as a systemic skeletal disease characterized by low bone mass and deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture, usually in the wrist, spine and hip.
Note that calcium itself cannot cure osteoporosis, but nutrition (calcium & vitamin D3) and physical activities can help reduce the risk. There is very little we can do to stimulate bone growth to offset age-associated bone loss. That's why it is important that children and adolescents take care of their bone health and achieve the highest possible bone mineral density (BMD), to prevent or overcome bone health issues later in life. People of all groups and ages should take care of their nutrition and physical activities to protect bone health, prevent injuries and preserve their quality of life.
Bones are the biggest calcium store
When there is not enough calcium in our blood we take it from our bones, because it is where most of it is stored in our body. If over the long run we are unable to replenish calcium from our diet, and if for any reason, our body is unable to absorb calcium effectively and deposit the minerals to form bones, there is higher risk of fragile bones, bone injuries and slow recovery.
Did you know that when pregnant mothers are unable to get enough calcium, their babies won't run out of calcium for growth because they can get calcium from the mothers' bones? What does that mean for expecting mothers? Also for everyone else who does not take in enough calcium through nutrition?
How to Maximize Bone Health
Nutrition - adequate calcium and vitamin D3
Physical activities. Impact and weight bearing exercises that put bones under strain can send signal for bone formation, examples are weight lifting, running, combat sports and resistance training
Sports that require lower body weight such as endurance, gymnastics, ballet and jockey are likely to be at risk of low bone mineral density (BMD), in which case resistance exercise should be encouraged for these athletes.
Limit alcohol, tobacco and anything that can negatively impact calcium absorption.
Recommended Daily Intake for Calcium
Adult male and female - 1,000 mg per day
51-70 years male 1,000 mg per day; 51-70 years female 1,200 mg per day
71+ years male and female - 1,200mg per day
Excessively high levels of calcium in the blood is called hypercalcemia, and can cause renal illness, calcification of blood vessels and soft tissues. The Tolerable Upper Intake for calcium is 2,500 mg per for adults 19-50 years, and 2,000 mg for adults 51+ years. Excessive intake can cause constipation, malabsorption of other vitamins such as iron, magnesium and zinc, kidney stones or kidney malfunction, cardiac arrhythmia.
Dietary Sources of Calcium
Dietary sources of calcium include dairy such as milk, cheese and yoghurt, fish such as sardines and salmon, and plants such as tofu made with calcium sulfate, leafy greens such as kale, chinese cabbage (pak choi) and broccoli. Note that spinach is not considered calcium rich because of the presence of oxalate which inhibits mineral absorption.
Spinach is not considered a calcium rich food because of the presence of the anti-nutrients oxalate and phytate that prevent the absorption of the mineral.
Follow A Wholesome Diet
In other words, the amount of calcium present in a food is not necessarily what your body will absorb. The key is to ensure that you eat a variety of foods across the board (meat, fish, vegetables) and limit processed junk (refined carbs, sugar and highly processed seed oils), you likely have the full set of nutrients (not just calcium) for your health (beyond your bones)
Supplementation
The two main forms of calcium supplements are carbonate and citrate. The carbonate form is better absorbed when taken with food, and citrate is absorbed well when taken with or without food. Since the body can only absorb a limited amount of calcium at one time, it is best to keep dosages to <500mg for greatest absorption.
What Affects Calcium Absorption
Vitamin D3 helps absorption and regulation of calcium and phosphorus in the body. We can make vitamin D3 from sunlight, we can also obtain vitamin D3 from foods such as canned tuna, sardines, dairy, and supplements.
Oxalate or oxalic acid in spinach inhibits calcium absorption, one way to remove oxalate is to wash the vegetables with boiling water and rinse. Cooking and rinsing can help remove oxalate. Combining leafy greens with calcium rich foods like cheese (or salmon!) can help to mitigate issues with oxalates, examples include broccoli & cheese and creamed spinach.
Too much iron intake can inhibit calcium absorption due to mineral-mineral interactions.
Medication. Antacids that contain aluminium and magnesium can increase excretion of calcium through urine and mineral oil can decrease calcium absorption. Similarly, calcium can also interact and affect the effective of medications (e.g. certain classes of antibiotics).
Who Are At Risk of Calcium Deficiency
Postmenopausal women due to lower estrogen levels to protect their bones.
Women with amenorrhea and/or anorexia nervosa, generally have lower bone mineral density, menstrual irregularities and higher risk (and a history) of stress fractures
People with lactose intolerance or allergic to milk or dairy.
Vegans have higher risk of calcium deficiency than vegetarians because they do not consume dairy. Vegans tend to rely on plants and leafy greens as a source of minerals (e.g. iron, calcium), but these also contain phytate/ phytic acid and oxalate/ oxalic acid which can greatly inhibit mineral absorption.
Calcium for Athletes
For athletes, the nutritional requirement for bone health is largely the same as the general population. Here are a few more specific issues.
Low energy availability (LEA). Inadequate energy intake generally reflects inadequate intake of minerals and micronutrients, which can affect bone health and increase the risk of bone injuries, lower bone mass and strength. When energy is restricted, the body will prioritize critical functions such as cardiovascular over bone health, and may slow down bone formation.
Female athletes who suffer amenorrhea or menstrual dysfunction due to LEA are at risk. Another term called "the female athlete triad" relates to the combination of disordered eating, amenorrhea and osteoporosis, which is similar to LEA as it relates to insufficient energy and nutrient intake to support athletes' health, performance and recovery.
Athletes in sports that favour lower body mass, non weight bearing and mostly training indoors are at higher risk of lower BMD, e.g. long distance running, ballet, cycling and swimming.
Vegans are more at risk than vegetarians because of greater consumption of plants containing oxalate and phytate can inhibit calcium absorption (see above).
More About Calcium and Bone Health
There is no evidence to suggest a high protein intake negatively affects bone health. In fact protein intake may have a small positive impact on bone mass and lower fracture risk by supporting the growth of muscle mass and function.
Whilst kidney stones are mostly made up of calcium oxalate, and some studies suggest an association between calcium supplementation and the risk of kidney stones. For the majority of healthy people, risk factors such as high intakes of oxalates from food and lower intakes of fluid may be more important than calcium intake.
Caffeine can increase urinary calcium excretion and lowers calcium absorption in the gut, however research shows that individuals with adequate calcium intake can compensate such loss.
Alcohol can negatively affect bone formation in adolescents and lower their ability to reach peak bone mass. Alcohol can also impair post exercise muscle recovery.
Other key nutrients for bone health include protein, magnesium, phosphorus, vitamin D, potassium, and fluoride. In addition, silicon, manganese, copper, boron, iron, zinc, vitamin A, vitamin K, vitamin C and B support numerous metabolic processes important for bone health.
Anything else?
I hope you find the above informative and useful for maintaining your bone health. If you have any questions or ideas about this topic, please share with me.
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References
Calcium. Fact Sheet. National Institutes of Health Office of Dietary Supplements
Calcium and Vitamin D
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Bone Health
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