Calcium is vital for maintaining strong bones and teeth, as well as supporting crucial functions like blood clotting, muscle contraction, and nerve function. Understanding which foods contain calcium is essential for overall health. This guide provides a comprehensive overview of calcium-rich foods and important information about calcium intake.
Assortment of calcium-rich foods including cheese, nuts, broccoli, canned fish, and milk displayed on a wooden board, emphasizing the diversity of dietary calcium sources.
The Importance of Calcium
The body tightly regulates calcium levels. When blood calcium levels are low, parathyroid hormone (PTH) signals the bones to release calcium. PTH also activates vitamin D to enhance calcium absorption in the intestines and signals the kidneys to reduce calcium loss through urine. Conversely, when calcium levels are sufficient, calcitonin lowers blood calcium by inhibiting calcium release from bones and promoting calcium excretion by the kidneys.
Recommended Daily Calcium Intake
The Recommended Dietary Allowance (RDA) for calcium varies by age and gender:
- Women (19-50 years): 1,000 mg daily
- Women (51+ years): 1,200 mg daily
- Pregnant and lactating women: 1,000 mg daily
- Men (19-70 years): 1,000 mg daily
- Men (71+ years): 1,200 mg daily
Calcium and Health: Benefits and Considerations
Blood Pressure
Some studies suggest a potential link between total calcium intake (from both food and supplements) and lower blood pressure. However, due to limitations in study designs, current evidence isn’t strong enough to recommend increasing calcium intake above the RDA for treating high blood pressure. More extensive research is needed to determine the impact of increased calcium intake or calcium supplements on high blood pressure.
Cardiovascular Disease
Research has raised concerns about potential risks of calcium supplements on heart health. High doses of supplements might cause hypercalcemia, potentially leading to blood clots or hardening of the arteries. However, guidelines from the National Osteoporosis Foundation and the American Society for Preventive Cardiology suggest that calcium from food or supplements has no significant relationship (positive or negative) with cardiovascular disease in healthy adults. It’s advised to stay within the Upper Limit (UL) of 2,000-2,500 mg daily from all sources.
Bone Health
Calcium is crucial for bone health. Bones are constantly being remodeled, with osteoblasts building bone and osteoclasts breaking it down. Adequate calcium intake and physical activity help ensure that bone production exceeds destruction until around age 30. After that, bone loss may occur. While sufficient dietary calcium can slow bone loss, it may not completely prevent it. Calcium absorption decreases with age, so high calcium intake may not always resolve bone loss issues.
Studies on calcium intake and bone density in postmenopausal women have varied results, potentially due to factors like only assessing calcium from supplements and not accounting for hormone replacement therapy. Some trials have shown that higher calcium intakes (often through supplements) are linked to improved bone density and slightly reduced risk of hip fractures. The RDA for calcium is higher for postmenopausal women due to these findings.
Colorectal Cancer
Epidemiological studies suggest that high calcium intakes (from food and/or supplements) may play a protective role against colorectal cancer. Randomized controlled trials with calcium supplements have shown mixed results, possibly due to short durations.
- A Cochrane review found that 1,200 mg of elemental calcium daily for about 4 years reduced the incidence of new colorectal adenomas by 26%.
- However, a trial from the Women’s Health Initiative found no difference in colorectal cancer incidence with 1,000 mg of elemental calcium and 400 IU vitamin D daily for about 7 years. This study noted that participants already had high calcium intake at the start.
The World Cancer Research Fund and the American Institute for Cancer Research suggest that calcium supplements of more than 200 mg daily and high-calcium dairy intake likely decrease the risk of colorectal cancer. This may be due to calcium binding to toxic substances in the colon or the protective effects of certain bacteria in dairy foods.
Kidney Stones
Contrary to previous beliefs, not eating enough calcium-rich foods can increase the risk of kidney stone formation. Studies have shown that high intake of calcium foods decreases the risk of kidney stones in women, but calcium in supplement form may increase risk. Calcium-rich foods, particularly dairy, reduce the absorption of oxalates, which contribute to calcium-oxalate stones.
Key Food Sources of Calcium: Which Foods Contain Calcium?
Calcium is abundant in various foods:
- Dairy Foods: Milk, cheese, yogurt are excellent sources.
- Leafy Greens: Kale, collard greens, and turnip greens contain calcium, but bioavailability varies.
- Beans: White beans, kidney beans, and soybeans.
- Nuts: Almonds are a good source, although their bioavailability is lower.
- Fortified Foods: Orange juice, plant-based milks, and cereals are often fortified with calcium.
- Fish with Edible Bones: Sardines and canned salmon are good sources.
- Tofu: Calcium-set tofu.
Bioavailability of Calcium
Calcium bioavailability refers to the amount of calcium that the body can absorb and use. Dairy foods have a bioavailability of about 30%. Plant foods like bok choy contain less calcium overall but have a higher bioavailability (around 50%). Spinach, while high in total calcium, has low bioavailability due to its high oxalate content. It’s important not to rely on spinach as a primary calcium source.
Signs of Calcium Deficiency and Toxicity
Deficiency
A serious calcium deficiency, known as hypocalcemia, can result from kidney failure, digestive tract surgeries, or certain medications. Symptoms include muscle cramps, numbness, abnormal heart rate, and poor appetite. Long-term inadequate calcium intake can lead to osteopenia and osteoporosis. Risk factors include menopause, amenorrhea, milk allergy, or lactose intolerance.
Toxicity
Too much calcium in the blood, or hypercalcemia, can result from exceeding the Upper Limit (UL) of 2,500 mg daily from food and supplements. Symptoms include weakness, nausea, shortness of breath, and heart palpitations. High doses of calcium can interfere with the absorption of other minerals like iron and zinc.
Conclusion
Knowing which foods contain calcium is crucial for maintaining optimal health. Prioritize a balanced diet with a variety of calcium-rich foods to meet your daily requirements. Consult with healthcare professionals for personalized advice, especially if you have specific health conditions or concerns about calcium intake.
