Calcium is the most abundant mineral in the body, with most of it in the bones and teeth. In addition to its role in the structure of bone and teeth, calcium has important roles in:
– Bone formation and remodeling (osteoclasts dissolve bone and osteoblasts synthesize new bone).
– Cell signaling (contraction and relaxation of blood vessels and muscles, nerve impulses, hormone secretion).
– Calcium is required for 7 vitamin K-dependent clotting factors.
Blood calcium levels are tightly regulated to a narrow range so blood levels are not a good measure of calcium status. Vitamin D is needed for proper calcium absorption. Parathyroid hormone acts on the kidney when blood calcium is low to increase active 1,25-OH D3 (calcitriol), which then promotes increased absorption of calcium and release of stored calcium from bone.
SYMPTOMS OF DEFICIENCY
Acute calcium deficiency would likely be the result of low parathyroid hormone that can be due to magnesium deficiency, kidney failure, or vitamin D deficiency. Symptoms may include muscle or nervous irritability, muscle spasms and cramps, or in severe cases, tetany.
Chronic calcium deficiency results in bone loss which causes rickets in children and osteoporosis or osteomalacia in both adults and children
As dietary protein increases, there is an increase in urinary excretion of calcium. Higher sodium intake has also been associated with increased urinary excretion of calcium. Kidney stones are typically calcium oxalate or calcium phosphate, and tend to occur in those with higher urinary excretion of calcium. Interestingly, higher dietary intakes of calcium actually lower urinary excretion of calcium making the standard recommendation for those who suffer from kidney stones to reduce calcium intake to be misguided. The recommendation should be to reduce protein and sodium intake and drink more water.
Adequate calcium seems to be protective against colorectal cancers, hypertension (especially pregnancy induced), and may reduce insulin resistance, being protective against type-2 diabetes.
Most people get their calcium from fortified cereals or dairy. It is however quite possible to get adequate calcium with a dairy free diet if you know what to eat.
Firm tofu (1/2 cup) 861
Collard greens (1 cup) 357
Turnip greens (1 cup) 197
Kale (1 cup) 187
Greens (1 cup) 100-300
Beans & legumes 100-200
Sardines (7 filets) 327
Seeds and nuts 70-100
Orange juice (1 cup -fortified) 500
Medium orange 65
Soy milk (1 cup) 300
Molasses (1 TBS) 178
Milk/ yogurt (8 ounces) 300-415
Cheese (1 ounce) 140-160
SAFETY AND TOXICITY
Toxicity has never been seen with foods although there is possibly increased prostate cancer in those with a very high dairy intake. Mild toxicity related to excessive intake of calcium supplements, or as part of antacids that are high in calcium, can result in loss of appetite, nausea, vomiting, constipation, abdominal pain, dry mouth, thirst, frequent urination. If calcium intake exceeds 2-4 grams daily on an ongoing basis, this can decrease the uptake of magnesium, zinc, iron, manganese, and other minerals, which can result in decreased reflexes, muscle weakness, ataxia, and anorexia.
TOLERABLE UPPER LIMITS
Infants Unknown (since they are in rapid bone growth – intake may be high but safe if just from breast milk or formula)
Children and adults 2500
The RDA for infants is listed as 210-170 mg, 500-1,300 mg children and 1300 mg for teens and adults. If your diet is low in calcium, I suspect you can avoid toxicity by keeping supplementation below 2000 mg a day and I would recommend only 1000 mg as supplements and add calcium rich foods. Remember to take a vitamin D supplement or you will not be absorbing much of the calcium from the diet or supplements.
Read about calcium and insulin resistance here…
Read about other sources of calcium here…
Read my blog on Vitamin D and calcium here…
Read my blog on calcium and heart disease here…