It’s safe to say pregnant women tend to experience an increase in size and a corresponding increase in blood volume to support the additional human being developed:
A healthy woman bearing a normal sized fetus, with an average birth weight of about 3.3 kg, will increase her plasma volume by an average of about 1250 ml, a little under 50% of the average non-pregnant volume for white European women of about 2600 ml.
If you have ever received IV fluids, you might have noticed plain water is not used. Rather, something termed Normal Saline, or fluid that has 0.9% Sodium Chloride (salt). With this information, would the salt demand for a pregnant woman increase or decrease?
Ok, the title of this post gave away my leaning here, but look at the scary headlines on the web:
From this article sans references:
According to Katherine Zeratsky, R.D., L.D., many people eat more sodium than necessary. You only need 200 to 500 mg a day to be healthy and to keep your body operating efficiently. In order to keep from consuming an unhealthy amount of sodium, focus on keeping your intake under 2,400 mg a day.
Seriously? 200-500 mg per day?
Little math: if 0.9% is the default salt concentration and she will have 3850 mL of plasma, that computes to 34 grams or 34,000 mg. 200 mg seems barely in the margin of error. Combined with the fact that we are told to constantly pound water, her salt concentration is bound to plummet right?
I have been clued into the low salt misinformation campaign for a while, but it was crystallized when I read the book The Salt Fix: Why the Experts Got It All Wrong–and How Eating More Might Save Your Life by James DiNicolantonio (a pharmacist of course!). Shortly after reading this book, I had the chance to share a passage on preeclampsia with someone experiencing it in her 8th month.
One myth that persists is that too much salt during pregnancy can lead to preeclampsia, a dangerous condition characterized by hypertension that can endanger both mother and child and lead to premature birth, among other complications. Over fifty years ago, a study published in the Lancet of more than two thousand pregnant women found that a low-salt diet, as compared to a high-salt diet, caused more miscarriages, premature babies (born prior to 34 weeks gestation), stillbirths, perinatal and neonatal deaths, edema, preeclampsia (previously known as toxemia), and bleeding. 55 And since there was less preeclampsia in those on the high-salt diet, it was decided later that cases of preeclampsia would be treated with extra dietary salt. Between the end of May and the end of September 1957, twenty-eight women were diagnosed with what was then known as “toxemia of pregnancy.” Eight were not given extra salt, while the other twenty were advised to ingest more dietary salt. All of the twenty women treated with extra salt improved, and all gave birth to healthy, full-term babies. An account of the study said, “the larger the dose of salt taken, the quicker and more complete was the recovery. The extra dose of salt had to be taken up to the time of delivery; otherwise the symptoms of toxemia recurred.” In other words, giving more salt treated preeclampsia rather than causing or worsening it (a common misconception). Consider this account from the researcher (from the study published in the Lancet): Sixteen patients were advised to measure out each morning four heaped teaspoonfuls of table salt and to see that by night they had taken all of it. It was calculated that they took about 200– 300 grams of salt daily [emphasis added]. The larger the amount taken the quicker was the recovery. They found it easiest to take the bulk of this salt in orange-juice, lemonade, or lime-juice, the remainder being put on their food. They were visited daily until all symptoms had disappeared. All of them recovered completely and continued well on at least three heaped teaspoonfuls of table salt a day. None of them had an infarcted placenta, and all gave birth to live full-term infants. 56 In contrast, certain side effects were also noted in the eight women who followed salt restriction, such as: severe backache, some [complained] of irritation of the skin of arms, legs, or abdomen, and some of weariness and stiffness in the limbs. Others complained of falling because their legs suddenly gave way under them. Sometimes this was so severe that they were afraid of going out of their houses or of crossing the road, in case they fell. These symptoms did not develop in the group given salt, and if they were present at the first examination they disappeared as soon as the women took more salt. 57 In other words, low-salt diets in pregnancy seem to lead to muscle weakness, particularly in the legs, which was treated by giving more salt. The authors concluded that extra salt in the diet seemed to be “essential for the health of a pregnant woman, her fetus, and the placenta.” 58 Because of the risks involved, ethics boards would not likely approve this kind of study today. With these kinds of results in only two small randomized controlled trials testing a low-salt versus a normal-salt diet in just a few hundred pregnant women, we may want to give strong reconsideration to the practice of recommending low-salt diets in pregnant women. 59 Another paper described the experience of a pregnant woman with elevated blood pressure and evidence of low aldosterone levels who was given 20 grams of salt per day, which led to a decrease in systolic and diastolic blood pressure of 16 and 12 mmHg, respectively. The authors concluded that low blood volume during pregnancy might be due to a reduced ability to produce aldosterone and that pregnant women would probably benefit from salt supplementation. 60 Another study confirmed these findings, saying they “support the importance of salt in normal pregnancy, a critical issue given the passionate campaigns to lower salt intake in the general population.” The researchers suggested that salt could be a “cheap and easy intervention,” particularly in areas with lower resources, to help avoid dangerous pregnancy conditions such as preeclampsia. 61 The possible harms of a low-salt diet in pregnancy or those trying to become pregnant are summarized in the list that follows. Consuming more salt may even help prevent pregnant women with normal blood pressure from transitioning into hypertension/ preeclampsia, as low plasma volume is a risk factor for developing hypertension in these women. 62 In fact, blood volume has consistently been found to be reduced in preeclampsia, and its improvement may be why salt is so helpful for treating preeclampsia in pregnancy. 63 THE POSSIBLE HARMS OF A LOW-SALT DIET IN PREGNANCY OR THOSE TRYING TO BECOME PREGNANT Reduced chance of becoming pregnant Increased chance of a miscarriage Increased risk of premature delivery Increased risk of infant mortality Increased risk of bleeding in the mother Increased risk of preeclampsia Increased risk of low-birth-weight babies who will become chronic salt cravers/ addicts with higher risk of obesity, insulin resistance, hypertension, and compromised kidney function
DiNicolantonio, James. The Salt Fix: Why the Experts Got It All Wrong–and How Eating More Might Save Your Life (p. 142). Potter/TenSpeed/Harmony. Kindle Edition.
Then this message came back the next morning from my patient:
FYI… I mixed and drank 1 tsp of salt in water twice yesterday & added more to popcorn last night. My BP this morning was 129/91 (previous two days were systolic: 140’s & diastolic: 100-110)
Pretty quick results.
There is so much bad information out there. Please seek multiple opinions before deciding on a path forward, especially with important conditions like pregnancy!