Calcium is the most common mineral in the human body. Calcium is a
nutrient in the news because adequate intakes are an important determinant
of bone health and risk of fracture or osteoporosis. Our nation suffers
from approximately 1.5 million fractures annually with an associated
health care cost of $13.8 billion.
Approximately 99% of total body calcium is in the skeleton and teeth
and 1% in blood and soft tissues. Calcium has four major biological
functions: 1) structural as stores in the skeleton, 2)
electrophysiological - carries charge during an action potential across
membranes, 3) intracellular regulator, and 4) as a cofactor for
extracellular enzymes and regulatory proteins. Calcium is present in
variable amounts in all the foods and water we consume, although the main
sources are dairy products and vegetables.
Deficiencies: Acute deficiency symptoms are avoided
because of the large skeletal stores. Prolonged bone resorption from
chronic dietary deficiency results in osteoporosis either by inadequate
accumulation of bone mass during growth or increased rate of bone loss at
menopause. Dietary calcium deficiency also has been associated with
increased risk of hypertension, preeclampsia, and colon cancer.
Dietary recommendations: The dietary recommendations
set by the 1997 National Academy of Science Panel on Calcium and Related
Nutrients are: 210 mg/d for 0-6 month olds, 270 mg/d for 6-12 month olds,
500 mg/d for 1-3 year olds, 800 mg/d for 4-8 year olds, 1300 mg/d for
individuals aged 9-18 years, 1000 mg/d for individuals aged 19-50 years,
and 1200 mg/d for individuals over the age of 51 years. No alterations for
pregnancy or lactation were recommended. The recommended upper level of
calcium is 2.5 g/day.
Food sources: Dairy products are the most
concentrated, well-absorbed sources of calcium. Few other foods are rich
sources of calcium. Foods which can contribute to dietary calcium include
firm tofu (chemically set with calcium), dried beans, kale, broccoli, and
bok choy. Calcium from oxalate rich foods such as spinach is generally
poorly absorbed. Phytates are slightly inhibitory to absorption. Since FDA
allows a label claim relating calcium to prevention of osteoporosis, some
fortified foods have become available on the market.
Toxicity: Symptoms of calcium toxicity are largely
anecdotal. Excess calcium supplementation has been associated with some
mineral imbalances such as zinc.
Recent research: Increasing calcium intakes during
adolescence increases calcium accretion up to 1300 mg/day and increases
bone mineral content. Even in children, bone density determines fracture
risk. Calcium and vitamin D supplementation in the elderly reduces
incidence of fracture.
