Electrolytes while pregnant or breastfeeding: What you need to know

Ah, the joys of pregnancy and breastfeeding. Your body and baby crave more of just about everything: calories, protein, vitamins, minerals, sleep. I’ve been through it twice, and I probably don’t have to tell you that it wasn’t easy. One thing that was particularly frustrating for me was my milk supply while nursing my first daughter, Zoe. I wish I had known more about electrolytes during this time, especially how sodium affects lactation.

I wasn’t intentionally restricting salt, but in retrospect I think I would have benefited from prioritizing it. Unfortunately, many women following conventional wisdom actively limit sodium to prevent preeclampsia, a condition of high blood pressure plus swollen hands and feet that can develop halfway through pregnancy. I say “unfortunately” because sodium is important for both mother and child, and not just for milk production.

I’ll dig into that and related research on sodium for prenatal and postnatal health in this article. I’ll also cover other electrolytes like magnesium, potassium, calcium, and phosphorus. My hope in sharing what I’ve learned is to help other women navigate their own extraordinary journeys to motherhood.

Sodium Needs During Pregnancy

Electrolytes are minerals that conduct electrical charges in your body, maintain fluid balance, aid in blood flow, regulate blood pressure, build bone, and influence a wide range of hormones. As with most other nutrients, electrolyte needs increase during pregnancy and nursing.

Adequate sodium intake is particularly essential for a developing fetus. Restricting sodium intake below 3 grams per day has been shown to slow growth, reduce birth weight, shrink the cardiovascular system, and impair kidney function in the fetus. As a result, the baby is more likely to develop high blood pressure later in life. So, why do some people recommend salt restriction during pregnancy? Let’s dig in. 

Salt Restriction and Preeclampsia Risk

Many believe restricting sodium helps women avoid preeclampsia, a pregnancy complication marked by swelling of the hands/feet and high blood pressure. Preeclampsia is linked to changes in the renin-angiotensin-aldosterone system, a trio of hormones that regulate blood pressure and fluid balance. It’s also linked to pregnancy-related problems such as low birth weight. Let’s review several studies on preeclampsia and salt intake:

• A 2005 Cochrane review found no link between salt intake and preeclampsia occurrence in 603 pregnant women. The authors conclude: “In the absence of evidence that advice to alter salt intake during pregnancy has any beneficial effect for prevention of pre-eclampsia or any other outcome, salt consumption during pregnancy should remain a matter of personal preference.”
• A 2018 review similarly concluded that there’s “no convincing evidence” that salt intake influences hypertension or preeclampsia risk.
• A 2019 paper did find a connection between salt intake and preeclampsia. Of 569 pregnant Danish women, those who consumed over 2.4 grams of sodium per day were slightly more likely to be diagnosed with preeclampsia than those who consumed less than that. For any stat geeks out there, the “P-value” of this effect was 0.04 — just barely enough to achieve statistical significance.
• A 2020 review following 62,774 women found that higher sodium intakes (median 3.7 grams daily) correlated with a 2% risk of developing preeclampsia during pregnancy, while low sodium intakes (median 2.6 grams daily) clocked in at 1.6%.

So why did the final two papers find a weak (yet statistically significant) link between sodium intake and preeclampsia? It’s not exactly clear because the data is observational, but one possible explanation is that high-sodium diets also tend to be high in processed, sugary foods. Modern, hyper-palatable foods are high in sugar (and salt), and high sugar intakes are linked to increased risk of preeclampsia.

I’ll point out that women with preeclampsia, in addition to experiencing high blood pressure (hypertension), are also more likely to have low blood sodium levels compared to others. This correlation isn’t surprising since being low in sodium triggers hormonal changes that raise blood pressure. Therefore, increasing hypertensive pregnant womens’ sodium intake, perhaps counterintuitively, often lowers blood pressure.

Based on the available evidence, my preference would be for pregnant women not to restrict salt intake. There isn’t great data that avoiding salt reduces the risk of preeclampsia, but there is concerning data linking low-salt diets to fetal growth, birth weight, and other complications. That’s the best information we have right now — and it’s worth keeping an eye out for emerging research.

Sodium while Breastfeeding and Beyond

Babies need electrolytes too, most of which they get via breastmilk or formula. If you’re using formula, you’ll want to confirm that — like breast milk — it’s rich in electrolytes (for a comprehensive guide on infant nutrition, I highly recommend functional medicine practitioner Chris Kresser’s course The Healthy Baby Code).

A mom’s dietary sodium intake directly correlates with the amount of sodium in her milk. Sodium concentrations in human milk are elevated in the early stages of breastfeeding when the milk takes the form of colostrum, the antibody-rich “first milk” that seeds the infant’s immune system. Some research suggests that inadequate breast milk electrolytes could adversely affect the child’s future health.

Sodium is especially important for cognitive function down the road. In one study, giving salt supplements to prematurely born infants was linked to better motor function, IQ, and memory when these kids turned 10–13. This result doesn’t mean, however, that all babies should be given extra salt. Some evidence suggests that too much salt early in life can predispose them to future cardiovascular issues. My suggestion to nursing moms is to keep their own salt intake in moderate ranges and let their breast milk provide salt to their babies.

Salt status is also correlated with milk production volume. Some studies have suggested that sodium supplementation increases lactation in mammals, and dairy farmers have long known that increasing sodium boosts milk production in cows. On the human front, I’ve heard many stories from moms who insist that LMNT has increased their milk supply. I know that’s anecdotal, but it’s been such a common theme that it’s hard to ignore.

So, how much sodium do women need during pregnancy and while breastfeeding? The latest science shows that consuming 4–6 grams of sodium daily appears to be the sweet spot for optimal health outcomes and to avoid sodium deficiency in adults. Diet and lifestyle factors like exercise can increase those needs. Pregnant and nursing women may find they feel better with slightly more sodium to replace what’s going to their child. But since everyone is different, some women may need less. Test it out and find what feels right for you based on your energy levels and cravings (AKA if you find yourself craving salty foods, don’t be afraid to listen to that urge).

Other Electrolytes for Pregnancy and Nursing

Sodium isn’t the only electrolyte needed during this critical time. Here are a few others to pay attention to while pregnant and nursing.

• Potassium. Potassium balances the effects of sodium and helps women maintain healthy blood pressure during pregnancy. 3.5–5 grams of potassium per day is a solid range to shoot for; pregnant and nursing women should aim for the upper end. To hit this target, prioritize potassium-rich foods like avocados and meat, and supplement potassium chloride as needed.
• Magnesium. Pregnancy increases magnesium needs, and magnesium deficiency during pregnancy can affect fetal growth and spike the mother’s blood pressure. One study found that women supplementing 300 mg of magnesium daily had fewer pregnancy complications than those at 100 mg/day. 400–600 mg of magnesium daily is a good target. Similar to potassium, start with incorporating magnesium-rich foods into your diet like spinach and black beans. Supplementing with 300 mg magnesium malate daily can also help.
• Calcium. Calcium is the main mineral for building bone in the growing fetus. Interestingly, however, calcium supplementation does not appear to improve calcium status in pregnant women. The evidence-based recommendation is to get 1,000–1,300 mg of calcium daily from dietary sources such as dairy.
• Phosphorus. Phosphorus helps build bone and produce energy. Since it’s prevalent in many foods, deficiency is rare, so it’s unlikely you’ll need to supplement phosphorus.

Takeaways and Parting Thoughts

When a woman is pregnant or nursing, she needs enough sodium, potassium, and magnesium to support herself and her growing child. And while sodium is controversial, I believe the evidence points away from salt restriction during pregnancy. Other priorities worth mentioning include getting enough nutrients (especially protein), sleeping plenty, and listening to your body.

Lastly, try not to stress too much. There are plenty of things I wish I knew earlier in my journey to motherhood — we learn as we go, just like everybody else. On that note, I hope this article taught you something new to help you along your journey.