Calcium Functions
Labeled illustration of bone
Calcium is the most abundant mineral in the body and most commonly known for it's role in bone. Bone mineralization, the process of calcium adding to bone's strength and rigidity, is one of calcium's main roles. Calcium is stored in the bone and is the most abundant mineral in the body.
Calcium also has a number of other roles, including:
The body keeps calcium within the bloodstream under really tight control. The body doesn't let calcium become too high or too low. When we consume food with calcium, calcium is absorbed into the bloodstream. This will elevate the calcium in the bloodstream slightly, but the body immediately shifts this calcium to the bone to be used for mineralization. If calcium blood levels drop, then absorption within the intestines actually increases, pulling more calcium from the food in the intestines, into the bloodstream. In addition, when blood calcium levels are low, bone will be broken down and calcium is released into the bloodstream, to bring the level of blood calcium back up to its normal range.
Calcium also has a number of other roles, including:
- nerve transmission
- acid/base balance
- transport of ions
- blood pressure
- blood clotting
- muscle contraction.
The body keeps calcium within the bloodstream under really tight control. The body doesn't let calcium become too high or too low. When we consume food with calcium, calcium is absorbed into the bloodstream. This will elevate the calcium in the bloodstream slightly, but the body immediately shifts this calcium to the bone to be used for mineralization. If calcium blood levels drop, then absorption within the intestines actually increases, pulling more calcium from the food in the intestines, into the bloodstream. In addition, when blood calcium levels are low, bone will be broken down and calcium is released into the bloodstream, to bring the level of blood calcium back up to its normal range.
Calcium Deficiency - Osteoporosis
Osteoporotic versus normal bone
Osteoporosis is a reduction of bone mass. The major consequence of osteoporosis is fracture. In the image to the right normal bone is depicted compared with osteoporotic bone. You can appreciate the thin matrix of bone with more space and less density.
We reach peak bone mass by the age of 18, but bone continues to build at a slower rate up until the age of 30 years. At thirty years of age, bone mass starts declining in both men and women. After menopause, estrogen diminishes in women and bone loss accelerates rapidly for about 6-8 years. Bone loss continues after the period of accelerated loss, but not as quickly.
According to the International Osteoporosis Foundation, 44 million people in the U.S. have or are developing osteoporosis and 1.6 million hip fractures occur worldwide each year. About 250,000 older adults are hospitalized for hip fractures every year. An analysis of the Nationwide Inpatient Sample Data found that osteoporotic fractures cost over $5 billion dollars annually, which is surprisingly more than the annual cost for hospitalizations for heart attacks (myocardial infarctions).
According to the Center for Disease Control (CDC), 54% of postmenopausal caucasian women are osteopenic (this means they have low bone density) and 25% have osteoporosis; 44% of men over 65 are ostepenic, but only 6% of men have osteoporosis. About half of the US population over 65 years of age has low bone mineral density. Mexican- American adults and non-hispanic Caucasian women have the greatest incidence of osteoporosis.
Although calcium deficiency is associated with low bone mineral density, there are many factors that contribute to the development of osteoporosis. Low vitamin D levels, a sedentary lifestyle, excessive intake of alcohol, tobacco use/cigarettes, extremely low calorie intakes or eating disorders will all increase the risk of osteoporosis.
We reach peak bone mass by the age of 18, but bone continues to build at a slower rate up until the age of 30 years. At thirty years of age, bone mass starts declining in both men and women. After menopause, estrogen diminishes in women and bone loss accelerates rapidly for about 6-8 years. Bone loss continues after the period of accelerated loss, but not as quickly.
According to the International Osteoporosis Foundation, 44 million people in the U.S. have or are developing osteoporosis and 1.6 million hip fractures occur worldwide each year. About 250,000 older adults are hospitalized for hip fractures every year. An analysis of the Nationwide Inpatient Sample Data found that osteoporotic fractures cost over $5 billion dollars annually, which is surprisingly more than the annual cost for hospitalizations for heart attacks (myocardial infarctions).
According to the Center for Disease Control (CDC), 54% of postmenopausal caucasian women are osteopenic (this means they have low bone density) and 25% have osteoporosis; 44% of men over 65 are ostepenic, but only 6% of men have osteoporosis. About half of the US population over 65 years of age has low bone mineral density. Mexican- American adults and non-hispanic Caucasian women have the greatest incidence of osteoporosis.
Although calcium deficiency is associated with low bone mineral density, there are many factors that contribute to the development of osteoporosis. Low vitamin D levels, a sedentary lifestyle, excessive intake of alcohol, tobacco use/cigarettes, extremely low calorie intakes or eating disorders will all increase the risk of osteoporosis.
Recommended Intake for Calcium
Most adult men and women need 1,000 mg per day. Post menopausal women need 1,200 mg per day.
Age |
Amount of Calcium |
Infants 0-6 months |
200 mg |
Infants 6-12 months |
260 mg |
Children 1-3 years |
700 mg |
Children 4-8 years |
1000 mg |
Pre-Teen & Teens 9-18 years |
1,300 mg |
Males 19-70 years |
1,000 mg |
Males > 70 years |
1,200 mg |
Females 18- 50 |
1,000 mg |
Females 51+ |
1,200 mg |
Dietary Sources of Calcium
Milk is one of the most important sources of calcium in the United States. It is affordable and available. Although most people equate milk with calcium and strong bones, it's not necessary to consume milk to obtain adequate calcium.
Different foods have different absorption rates for calcium. Some foods contain anti-nutrients, such as phytates and oxalates, which inhibit the absorption of calcium. This mean the food may contain a lot of calcium, but very little will actually enter the body and be available to the cells for use. Spinach and rhubarb contain high amounts of oxalates, which means the calcium in these foods is not well absorbed.
Broccoli, bok choy, cabbage and turnip greens have lower amounts of calcium, but higher absorption rates. For example, milk has about 300 mg per cup, but only about 100 mg of calcium is absorbed. Turnip green appear to have much less calcium per cup, only 200 mg, yet 100 mg is also absorbed. Despite having a lower amount of calcium, the higher absorption rate allows for an equivalent amount of calcium to be absorbed as would be from milk.
Non-dairy whole (or lightly processed) food sources of calcium include:
Different foods have different absorption rates for calcium. Some foods contain anti-nutrients, such as phytates and oxalates, which inhibit the absorption of calcium. This mean the food may contain a lot of calcium, but very little will actually enter the body and be available to the cells for use. Spinach and rhubarb contain high amounts of oxalates, which means the calcium in these foods is not well absorbed.
Broccoli, bok choy, cabbage and turnip greens have lower amounts of calcium, but higher absorption rates. For example, milk has about 300 mg per cup, but only about 100 mg of calcium is absorbed. Turnip green appear to have much less calcium per cup, only 200 mg, yet 100 mg is also absorbed. Despite having a lower amount of calcium, the higher absorption rate allows for an equivalent amount of calcium to be absorbed as would be from milk.
- Milk = 300mg per cup = 100mg absorbed
- Turnip greens = 200mg per cup = 100 mg absorbed.
Non-dairy whole (or lightly processed) food sources of calcium include:
- salmon with bones
- soybeans
- tofu with calcium sulfate
- collard and turnip greens
- kale
- bok choy
Calcium and Phosphorus Video
References
- Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Elements. Food and Nutrition Board, Institute of Medicine, National Academies. United States Department of Agricultural. Last accessed March 23, 2016. https://fnic.nal.usda.gov/sites/fnic.nal.usda.gov/files/uploads/recommended_intakes_individuals.pdf
- Non Diary Sources of Calcium. Choose MyPlate. Last accessed March 23, 2016. http://www.choosemyplate.gov/dairy-calcium-sources
- Looker AC, Frenk SM. Percentage of Adults Aged 65 and Over With Osteoporosis or Low Bone Mass at the Femur Neck or Lumbar Spine: United States, 2005–2010. National Center for Health Statistics. Center for Disease Control. Page last updated: August 13, 2015. Last accessed April 4th, 2016. http://www.cdc.gov/nchs/data/hestat/osteoporsis/osteoporosis2005_2010.htm
- Facts and Statistics. International Osteoporosis Foundation. Last accessed April 4th, 2016. http://www.iofbonehealth.org/facts-statistics#category-23
- Hip Fractures Among Older Adults. Center for Disease Control. Last accessed April 4th, 2016. http://www.cdc.gov/homeandrecreationalsafety/falls/adulthipfx.html
- Singer A, et al. Burden of Illness for Osteoporotic Fractures Compared With Other Serious Diseases Among Postmenopausal Women in the United States. Mayo Clin Proc. 2015;90(1):53-62.
- Food Sources. Calcium. Minerals. Linus Pauling Institute Micronutrient Information Center. http://lpi.oregonstate.edu/mic/minerals/calcium#sources. Last updated August, 2014. Last accessed April 13, 2016.
- Osteoporosis locations by BruceBlaus on Wikipedia, CC BY-SA-4.0.
- Cross section of bone by Pbroks13 on Wikipedia, CC BY 3.0.