Sodium (and Salt)
Research on sodium during pregnancy is more abundant than most other nutrients, but there are still several unknowns. The pregnant body handles sodium and water differently than those who are not pregnant, and this mechanism is still not understood.
While blood pressure is strongly linked to sodium intake in individuals who are not pregnant, this does not appear to be the case during pregnancy. In fact – some researchers advocate that a salt-restricted diet (outside of normal limitations) has no benefit during pregnancy and is likely unnecessary in healthy, normal pregnancies.
However, excess sodium is still a concern, and it is important for general health that pregnant women stay within 1,500 to 2,300 milligrams/day.
If pregnant women have high blood pressure, or have concerns about their sodium intake during pregnancy, they should speak with their health care provider (HCP).
Note: Due to the reemergence of iodine deficiency, it is recommended that women switch their salt from kosher/sea salt to table (iodized salt). Read more below.
Background
Sodium is an essential nutrient involved in the regulation of fluid, electrolyte balance, and blood pressure, and assists in the conduction of nerve impulses and muscle contraction.
Sodium is one of the chemical elements found in salt (40% sodium and 60% chloride); salt is used to flavor and preserve food, increase the shelf life of foods, and help prevent bacteria growth.
Humans only require a small amount of sodium each day to function. Too much sodium in the diet can lead to high blood pressure, heart disease, and stroke.
Too much sodium is difficult for the kidneys to filter, and sodium builds up in the blood, leading to high blood pressure – which then leads to other health problems.
Numerous international government, health, and academic institutions recommend that adults limit their daily sodium intake to 1,500 milligrams (mg) (less than one teaspoon). However, intake of sodium higher than this recommendation is very common, as a well-balanced and varied diet usually contains more than this amount.
Pregnancy
The correct balance of water and salt are critical for blood volume expansion during pregnancy.
Total blood volume during pregnancy increases by about 1.5 liters (almost 40 to 50% increase, or about 1,250 milliliters) to support fetal and placental development and protection from blood loss during delivery.
Most of this expansion is plasma (a component of blood). For this increase to occur, pregnant women must accumulate and retain a significant amount of sodium and water, but how this is regulated by the body (i.e. kidneys) is not understood.
However, the kidneys may start the process. Early changes in the kidneys lead to faster filtering and increased urination which then leads to greater thirst. Increased fluid intake (i.e. drinking water) reduces sodium levels in the blood, so the body begins to retain sodium – leading to retention of fluid. The body retains an extra 6 to 8 liters worth of fluid during pregnancy (read Swelling).
In individuals who are not pregnant, a strong link exists between sodium intake and blood pressure, but this relationship during pregnancy is unclear.
Numerous studies from around the world have not been consistent on whether a low-sodium diet prevents or cures high blood pressure during pregnancy; some studies show no effect at all and conclude that sodium restriction is unnecessary during pregnancy.
It is possible that pregnancy allows a woman to regulate sodium differently, with a balance that is likely uniquely regulated by the kidneys and blood vessels. But while the mother may not be affected by varying levels of sodium, it could affect the fetus later in life, but this is still being studied.
It is advised that pregnant women stay within the same sodium limits as non-pregnant individuals, and aim to ingest below 2,300 mg/day, or, ideally, less than 1,500 mg/day. It is currently estimated that most individuals in the United States consume over 3,400 mg/day.
Deficiency
Although the sodium and water relationship is not completely understood, pregnant women can experience sodium deficiency through diarrhea, uncontrollable vomiting, extreme and prolonged sweating (overheating), and excessive use of diuretics.
However, low sodium status (hyponatremia) is also not well understood during pregnancy. There are case reports of this occurring with high amounts of intravenous fluids during labor, or by women drinking a significant amount of fluids in a short period of time.
Hyponatremia may cause nausea, vomiting, headache, and if severe – convulsions. Hyponatremia is treated with fluid restriction or hypertonic solution given intravenously, which contains sodium chloride (salt).
Food Sources
Most sodium in American diets comes from processed and manufactured food; a food does not have to taste salty to contain sodium (bread may contain traces to several hundred milligrams of sodium).
The average diet gets almost half of its sodium content from breads and rolls, cheese, cold cuts and cured meats, mixed meat dishes, mixed pasta dishes, pizza, poultry, hamburgers, hot dogs, chips, crackers, popcorn, pretzels, and soups.
Low salt foods are those which contain less than 120 mg of sodium per 100 g of food; high salt foods contain more than 600 mg of sodium per 100 g of food.
Foods naturally low in sodium are fruit, vegetables, oils, and cereals.
Action
Women who are concerned about their sodium status during pregnancy should speak with their HCP. Women should also consider discussing their overall diet with their HCP, who may be able to point out areas of potential nutrient deficiencies, or possible ways to improve their diet during pregnancy.
Unless specifically instructed by their HCP, there is currently no evidence pregnant women, in general, need to restrict their salt intake. However, this does not mean women can ingest higher sodium foods.
Pregnant women still need to remain within suggested limits (2,300 mg or below), and consider switching from kosher or sea salt to iodized table salt during their pregnancy.
Partner/Support
Although pregnant women do not need to restrict their salt intake, it is still important to avoid high sodium diets/meals for overall health. Partners can support pregnant women in this regard by eating healthier overall and supporting women in their desire to do the same.
Partners can also lead the way in cooking more at home (if possible), eating out less and making smarter choices, and remaining active together.
Resources
Sodium in Your Diet (U.S. Food and Drug Administration)
Sodium (American Heart Association)
Top 10 Sources of Sodium (U.S. Centers for Disease Control and Prevention)