Some people love the taste of salt. It's the first condiment they reach for. They also devour chips, popcorn, pretzels and the other snack foods rich in salt.
It turns out that people's preference for salt may have been imprinted while they were still in their mother's womb, according to University of Washington psychologists. Researchers Ilene Bernstein and Sue Crystal have found a link between people's salt preference and the level of morning sickness experienced by their mothers when they were pregnant.
Studying 16-week-old infants, the UW researchers found that babies whose mothers suffered moderate to severe nausea and vomiting in early pregnancy showed a greater preference for salt-water solutions than did babies whose mothers experienced mild or no morning sickness.
In earlier work, Bernstein and Crystal showed a similar pattern of salt preference among young adults. They found that the adult children of mothers who reported moderate or severe morning sickness had higher self-reported salt use, salt intake in the laboratory and preference for salty snack food than the offspring of women who had mild or no symptoms.
"It is astonishing that something that happened prenatally and is so common can have such a strong impact on infant preference and can have enduring consequences," said Bernstein, a professor of psychology who studies taste function and preference.
Heavy salt intake is related to and considered a risk factor for hypertension, and many people on low-salt diets have trouble staying on their diets because they find the food to be unpalatable.
The infant study, published in the current issue of the journal "Appetite," was conducted as part of Crystal's doctoral dissertation. She is now a post-doctoral fellow at the Monell Chemical Senses Center in Philadelphia. Nearly two-thirds of pregnant women suffer the symptoms of morning sickness and Bernstein said it is the dehydration associated with vomiting that seems to be the key in shaping a fondness for salt.
"Fluid depletion in the mother triggers the hormonal system in the blood and kidneys to restore the normal fluid level," explained Bernstein. "We don't know if these hormones cross the placental barrier and affect the baby or if dehydration causes the baby to release its own hormones to restore the fluid balance. These hormones can have powerful effects on the brain.
"Normally, morning sickness is not treated, but people are treated for dehydration by replacing fluids and salt. We don't know what other systems morning sickness might be affecting."
Crystal and Bernstein conducted two tests with 16-week-old infants who had no experience with food aside from formula or mother's milk.
In the first, small, measured amounts of three solutions -- distilled water, 0.6 percent salt water and 1.2 percent salt water -- were squirted into the babies' mouths. The babies' facial expressions, ranging from grimaces to licking happily, were later coded by observers who didn't know what solutions the infants were drinking. In the second test, the infants were given bottles filled with 20 milliliters of the same three water solutions for one minute or until they rejected a bottle. The amount of water consumed was then calculated.
In both tests, infants whose mothers suffered from moderate to severe morning sickness exhibited a stronger preference for the 1.2 percent salt solution than did the babies whose moms had little or no morning sickness. Bernstein described this solution as having a taste similar to the water people use in gargling. It isn't as salty as tomato juice or chicken soup, but would taste saltier than mother's milk or human saliva.
For the study, mild morning sickness consisted of vomiting once or twice during a pregnancy. Moderate to severe vomiting ranged from once every other day for at least one week to two and three times a day for three weeks.
"Admittedly, the connection between salt preference and morning sickness is unusual," said Bernstein. "But I think it gives us a window on how taste preferences are shaped."