What is preeclampsia?
Preeclampsia is a complication of pregnancy that is characterised by hypertension (high blood pressure) and proteinuria (protein in the urine). Preeclampsia usually occurs after 20 weeks of pregnancy in women who had normal blood pressure prior to pregnancy (1).
Preeclampsia that is unmanaged can lead to serious health complications for both mother and baby including preterm birth, stillbirth, low birth weight, placental abruption and elevated liver enzymes (1).
The only known cure for preeclampsia is delivery of the placenta. The condition is managed during pregnancy through the use of blood pressure lowering medications until the baby is developmentally mature enough to be delivered (2).
Research has shown that women who are more susceptible to hypertension and other cardiovascular conditions usually present with lower calcium intake than healthy women (3).
The World Health Organisation (WHO) have provided guidelines recommending routine calcium supplementation during pregnancy to prevent preeclampsia. The guidelines state, “In populations where calcium intake is low, calcium supplementation as part of antenatal care is recommended for the prevention of preeclampsia among pregnant women.”
What’s the mechanism behind calcium and preeclampsia?
Research has shown that calcium supplementation can halve the risk of developing preeclampsia in pregnant women with a low calcium intake (4).
Calcium intake may regulate blood pressure by modifying intracellular calcium in vascular smooth muscle cells and by varying vascular volume through the renin–angiotensin–aldosterone system. Basically, calcium helps blood vessels tighten and relax when they need to, thus affecting blood pressure (5).
How much calcium should I be getting and from where?
A high dietary intake of calcium has been associated with a decrease in blood pressure as well as a decreased risk of developing hypertension and preeclampsia (6). During pregnancy, calcium is in high demand. Around 30 grams of calcium is transferred to the foetus during gestation (2).
However, due to an increase in intestinal absorption of calcium, bone turnover and hormonal control over calcium homeostasis during pregnancy, the recommended dietary intake (RDI) of calcium during pregnancy is the same to a nonpregnant woman (2).
The Australian RDI for calcium for women (pregnant or not) aged between 19 and 50 years is 1000mg daily (7).
Some great food sources of calcium include:
· Hard cheeses – 28g of parmesan cheese contains 331mg calcium
· Milk – 1 cup of regular milk contains 304mg calcium
· Sardines – 105g tin of sardines contains 270mg calcium
· Salmon – 105g tin of salmon contains 198mg calcium
· Silverbeet – 1 cup of steamed silverbeet contains 174mg calcium
· Yoghurt – 100g of Greek yoghurt contains 130mg of calcium
· Poppy seeds – 1 tablespoon contains 126mg calcium
· Chickpeas – 1 cup of canned chickpeas contains 90mg calcium
· Almonds – 10 almonds contains 30mg calcium
Calcium supplements – how much and in what form?
The WHO recommends that the daily dose of calcium for pregnant women is 1.5-2g elemental calcium per day. This is much higher than the RDI of calcium and is based on clinical trials assessing the impact of calcium on preeclampsia risk during pregnancy (2).
Some clinical trials have demonstrated that supplementation with at least 1g of calcium daily can as much as halve a woman’s risk of developing preeclampsia during pregnancy (4). There is some conflicting information around calcium supplementation and so further research is necessary to determine the optimal and safest dosage of calcium supplements during pregnancy (4).
It is recommended that calcium supplementation be initiated at around 20 weeks’ gestation for those women that are at a higher risk of developing preeclampsia. Focussing on dietary intake of calcium throughout the duration of pregnancy is also important (2).
There are many different forms of calcium available in supplement form. Both calcium citrate and calcium carbonate are highly bioavailable forms when compared to calcium gluconate. Calcium carbonate is more affordable, yet calcium citrate bioavailability is less affected by meals (2).
This blog was written by Felicity Harvey as part of her internship.
References
1. Khaing W, Vallibhakara SAO, Tantrakul V, Vallibhakara O, Rattanasiri S, McEvoy M, et al. Calcium and vitamin D supplementation for prevention of preeclampsia: A systematic review and network meta-analysis. Nutrients. 2017;9(10):1–23.
2. Omotayo MO, Dickin KL, O’Brien KO, Neufeld LM, De Regil LM, Stoltzfus RJ. Calcium supplementation to prevent preeclampsia: Translating guidelines into practice in low-income countries. Adv Nutr. 2016;7(2):275–8.
3. de Souza EA, Momentti AC, de Assis Neves R, Minari TP, de Sousa FLP, Pisani LP. Calcium intake in high-risk pregnant women assisted in a high-complexity hospital. Mol Biol Rep [Internet]. 2019;46(3):2851–6. Available from: http://dx.doi.org/10.1007/s11033-019-04731-9
4. Hofmeyr GJ, Lawrie TA, Atallah ÁN, Duley L, Torloni MR. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2014;2014(6).
5. Villa-Etchegoyen C, Lombarte M, Matamoros N, Belizán JM, Cormick G. Mechanisms involved in the relationship between low calcium intake and high blood pressure. Nutrients. 2019;11(5):1–16.
6. Houston MC, Harper KJ. Potassium, magnesium, and calcium: their role in both the cause and treatment of hypertension. J Clin Hypertens (Greenwich). 2008;10(7 Suppl 2):3–11.
7. National Health and Medical Research Council (NHMRC). Calcium. Nutrient Reference Values for Australia and New Zealand. 2014.