Calcium, the most abundant mineral in the body, is required for a variety of critical functions that include muscular contraction, nerve transmission, intracellular signaling, and the maintenance of acid/base balance. Calcium also plays a structural role in bone and teeth where 99 percent of total body calcium is located.
Far from being static, bone undergoes constant remolding through resorption (osteoclasts) and deposition of new calcium (osteoblasts). There are no overt signs of calcium deficiency, because circulating levels are so tightly regulated. Low calcium intake, does however, lead to osteopenia and eventually osteoporosis.
The obvious high-risk group for calcium loss are postmenopausal women, whose bone loss accelerates with the loss of estrogen. Loss of bone mass is estimated at 3-5 percent the first years following menopause and then slows to around 1 percent per year around the age of 65. Other groups at risk are people who are white or of Asian descent, small frames, and any women who have experienced menstrual irregularities or amenorrhea for extended periods (such as extreme female athletes, or those who are chronically underweight).
Calcium absorption is typically poor, with humans absorbing only around 30 percent of calcium found in dairy and fortified foods (orange juice, tofu, soy milk), but absorption is much higher from certain green vegetables (bok choy, broccoli, kale). There is much discussion on forms of calcium and it appears that calcium citrate is absorbed better (approximately 24 percent better) than calcium carbonate, independent of meal intake.
The absorption of calcium is highest in infants and young children, but then decreases during adulthood.
Calcium absorption and excretion is well studied. It is notable that coffee increases excretion, but appears to have no long-term effects on bone mass. Alcohol also decreases absorption as well as decreasing the conversion of vitamin D to active form, but it is unknown how these effects influence bone quality.
|0–6 months*||200 mg||200 mg|
|7–12 months*||260 mg||260 mg|
|1–3 years||700 mg||700 mg|
|4–8 years||1,000 mg||1,000 mg|
|9–13 years||1,300 mg||1,300 mg|
|14–18 years||1,300 mg||1,300 mg||1,300 mg||1,300 mg|
|19–50 years||1,000 mg||1,000 mg||1,000 mg||1,000 mg|
|51–70 years||1,000 mg||1,200 mg|
|71+ years||1,200 mg||1,200 mg|
* Adequate Intake (AI)
Calcium intake (from all sources) appears to have an inverse relationship with risk of hypertension. While the evidence is weak, calcium consumption appears to work best in hypertensive subjects and amounts to a 2-4 mm/Hg drop in blood pressure.
Cancer of the Colon/Rectum
Several studies support the notion that higher consumption of calcium-containing foods; especially low-fat dairy products reduces risk of colon and rectal cancer., Other studies have shown that the combination of dietary and supplemental calcium has lasting effects (up to five years following cessation of supplementation) on risk of adenoma.
- A 16 year study included 87 998 women and 47 344 men who completed a food frequency questionnaires and provided information on medical history and lifestyle factors. Dietary information was updated at least every 4 years. An inverse association between higher total calcium intake greater and reduced risk (27 percent) of distal colon cancer was discovered. The effect was greatest in those consuming more than 1250 milligrams a day; no such association was found for proximal colon cancer.
- A 2008 Cochrane review suggested that while there have been positive results with many studies, the evidence isn’t clear enough to suggest the general use of calcium supplements to prevent colorectal cancer.
- A 2014 review summarized the relative risk from multiple studies and dosages and concluded that calcium was effective at reducing risk of adenomas over a wide range of dosages. When compared to a 550 mg/day dose, relative risk was: 0.92 (95% CI = 0.89-0.94) at 1,000 mg/day and 0.87 (95% CI = 0.84-0.90) at 1,450 mg/day. 
Calcium has proposed effects on the cardiovascular system through decreasing absorption and increasing excretion of lipids, lowering cholesterol, and by promoting calcium influx into cardiac muscle cells. Data from clinical studies, however, is contradictory with some large studies showing a positive effect for dietary and supplemental calcium, while others demonstrating no associations or a negative association with high intakes (over 1400 milligram/day). To date, no clinical trials have specifically tested the effect of calcium supplementation on cardiovascular disease as its primary endpoint, making a definitive conclusion difficult. When data is pooled from many studies, no association is uncovered.
Peak bone mass occurs around 30 years of age. This is followed by a steady decrease in bone mass for all populations, but is notably accelerated in postmenopausal women – especially in the first few years following end of menstruation. The higher the peak bone mass, the better one can delay serious bone loss later in life. This gives rise to the importance of building bone early in life and the importance of calcium in the diet. Supplemental calcium is a well-established method for mitigating bone loss. The US Food and Drug Administration authorize health claims related to calcium and osteoporosis as Health Claims Meeting Significant Scientific Agreement.
A review of 13 studies including 15,730 women showed a relative risk reduction of 35 percent using high dose calcium supplementation (greater than one gram). Another pooled analysis concluded that low dose calcium supplementation (less than a gram a day) also achieved risk reduction for hypertension of pregnancy.
Premenstrual syndrome (PMS)
A few small studies have shown a relationship between calcium intake and PMS symptoms.
- Young female college students were selected for study on response to a PMS questionnaire and randomized to receive 500 milligrams calcium two times a day or placebo for three months. Of the parameters studied, early tiredness, appetite changes, and depressive symptoms were significantly improved in the supplemental group.
- Thirty-three women with severe PMS symptoms were supplemented with 1,000 milligrams calcium a day and then crossed over to placebo. Seventy three percent of the women reported fewer symptoms during the treatment phase on calcium than on placebo.
While some early studies suggested a role for calcium intake (dietary and supplemental) in modulating weight gain,, more recent studies (including two large meta-analyses) have failed to uncover a substantial connection.,
The is an association between supplemental calcium intake and the risk of kidney stones. The Women’s Health Initiative study reported a 17 percent increase risk of kidney stones in postmenopausal women consuming 1,000 milligrams supplemental calcium a day. The Nurses’ Health Study also reported a positive association. The overall effect, however, is small. For most of the population, dietary changes (such as restricting animal protein and salt) have a much larger effect on reducing risk than increasing calcium. This association has not been reported with dietary calcium.
Calcium is a large molecule that has a potential to interact with many types of medications and other supplements. It is best to check with a health care practitioner or pharmacist before taking calcium along with any other medications.
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