Food is medicine: The science behind calcium

Key takeaways:

• Calcium supplementation could be beneficial for bone health and preeclampsia risk.
• However, the evidence is still uncertain.

Calcium supplementation may be helpful for bone health and, possibly, reducing preeclampsia risk, according to an expert.

Calcium is a nutrient that is involved with nerve and muscle function and is “required for building and maintaining strong bones,” Carol J. Haggans, MS, RD, scientific and health communications consultant at the NIH’s Office of Dietary Supplements (ODS), told Healio.

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For those aged 19 years and older, the recommended dietary allowance for calcium ranges from 1,000 to 1,200 mg per day, she said.

“Dairy products are the richest sources of calcium, but some vegetables, such as kale, broccoli and bok choy, also contain calcium,” Haggans said. “Calcium is added to some fortified foods such as some fruit juices. Many people in the U.S. consume less than recommended amounts of calcium, including some people who avoid dairy products.”

Calcium deficiencies can lead to lowered bone strength and osteoporosis, according to the ODS fact sheet, and calcium supplementation usually focuses on bone health.

Summary of evidence

A 2019 systematic review and meta-analysis of more than 122,000 people showed that calcium supplementation seems to be a promising strategy to reduce fracture risk. A combination supplement with calcium and vitamin D led to a 16% reduced risk for hip fracture (RR = 0.84; 95% CI, 0.72-0.97) and a 6% reduced risk for any fracture (RR = 0.94; 95% CI, 0.89-0.99).

However, a 2017 systematic review and meta-analysis including 51,145 participants showed that calcium supplementation did not reduce fracture risk among community-dwelling older adults because there was not a significant association between calcium and hip fracture risk (RR = 1.53; 95% CI, 0.97-2.42) compared with placebo.

“Calcium supplementation is used mainly for bone health in older adults,” Haggans said. “FDA has approved a health claim for the use of supplements containing calcium and vitamin D to reduce the risk of osteoporosis, but not all research supports this claim.”

The U.S. Preventive Services Task Force’s recommendation on calcium, vitamin D, or combined supplementation to prevent falls and fractures among community-dwelling adults is currently being updated, but in 2018, the task force decided against low doses of calcium or vitamin D for this use in post-menopausal women.

Additionally, a 2021 systematic review and meta-analysis including 3,222 participants showed that calcium fortification leads to increased calcium intake and offers small benefits in children’s bone health and height. In the intervention groups, calcium intake increased, and the effect was noteworthy in children: their femoral neck and hip bone mineral density increased 0.02 g/cm² (0.01-0.04) and 0.03 g/cm² (0.0-0.06) respectively, and height increased 0.83 cm (95% CI, 0.0-1.65) compared with controls. However, the authors wrote that more research is needed to confirm the findings.

Haggans also noted that calcium supplements may reduce the risk for preeclampsia among pregnant women with low dietary calcium intake. In fact, WHO recommends daily calcium supplementation (1.5-2 g) for this population to reduce preeclampsia risk, but the evidence is not entirely clear.

A 2018 meta-analysis published in the Cochrane Library, including 27 studies comprising 18,064 women, revealed that high-dose calcium supplements (at least 1 g/day) could lower the risk for preterm birth and preeclampsia, especially among women who have low calcium diets, but the evidence was low-quality. The researchers also wrote that the limited evidence regarding low-dose calcium supplementation indicates reductions in hypertension and preeclampsia, but should be confirmed in high-quality trials with larger populations.

Also, researchers who led a multicenter, double-blind, randomized, placebo-controlled trial published in The Lancet in 2019 found that calcium supplementation beginning before pregnancy and lasting until 20 weeks’ gestation did not lead to a significant reduction in preeclampsia compared with placebo. However, they also wrote that they could not completely rule out a small to moderate effect.

More information

For those aged 19 years and older, the tolerable upper intake level (UL) for calcium is 2,000 to 2,500 mg per day, Haggans said.

“The UL refers to intakes from all sources — food, beverages and dietary supplements,” she said. “High calcium intakes could cause kidney stones and might increase the risk of cardiovascular disease and prostate cancer, although not all studies agree.”

The ODS also offers other resources for health care providers and consumers. To learn more about calcium and other products, check out the ODS Fact Sheets.

Editor’s Note: Healio is highlighting the clinical value of various supplements. See other installments of the series here:

• Melatonin
• Omega-3
• Zinc and other supplements for immune function
• Vitamin D
• Ashwagandha
• Magnesium
• Folic Acid
• Vitamin B12
• Iodine

References:

• Calcium supplementation during pregnancy to reduce the risk of pre-eclampsia. https://www.who.int/tools/elena/interventions/calcium-pregnancy. Updated Aug. 9, 2023. Accessed Feb. 29, 2024.
• Cormick G, et al. Nutrients. 2021;doi:10.3390/nu13020316.
• Hofmeyr GJ, et al. Cochrane Database Syst Rev. 2018;doi:10.1002/14651858.CD001059.pub5.
• Hofmeyr GJ, et al. Lancet. 2019;doi:10.1016/S0140-6736(18)31818-X.
• Tai V, et al. BMJ. 2015;doi:10.1136/bmj.h4183.
• USPSTF. https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/vitamin-d-calcium-or-combined-supplementation-for-the-primary-prevention-of-fractures-in-adults-preventive-medication. Published April 17, 2018. Accessed March 5, 2024.
• Yao P, et al. JAMA Netw Open. 2019;doi:10.1001/jamanetworkopen.2019.17789.
• Zhao JG, et al. JAMA. 2017;doi:10.1001/jama.2017.19344.