While many studies have examined male salt consumption behaviors, less research has examined how these behaviors may differ among female subjects. To this end, a recent Nutrients journal study reviews differences in salt intake based on sex.
Study: Sex differences in salt appetite: Perspectives from animal models and human studies. Image Credit: mmpixels91 / Shutterstock.com
The innate appetite for salt among humans and animals is largely driven by the physiological need for sodium to maintain body fluid homeostasis and intracellular signaling. However, ‘salt cravings’ are also characteristics of various clinical and physiological conditions, such as during pregnancy, lactation, and stress. Even in non-deficient states, salt acts as a stimulus and facilitates various forms of learning.
Angiotensin II is a large hormone that directly acts on numerous organ targets, including the brain, to control salt and thirst appetite. Mineralocorticoids like aldosterone are also important hormones that regulate sodium levels by acting on the brain to induce thirst and salt hunger cues.
Despite the vast amount of studies that have been conducted to better understand how these different hormones regulate sodium appetite, most of these experiments have only been conducted in male rats, thus limiting the generalizability of these findings to female rats.
Sex differences and salt appetite
Exposure to different levels of estrogens, progestins, and/or androgens in both males and females has been shown to have a temporary impact on sodium intake when directly exposed to these hormones. Thus, the physiology of salt in both men and women, as well as their behavior in regard to the intake of this essential mineral, is likely independent of gonadal hormones.
Interestingly, in vivo studies in rats have consistently demonstrated that adult female rats will consume a greater amount of saline as compared to male rats. Furthermore, female rats will often elicit greater ingestive responses to sodium than male rats when participating in taste reactivity tests.
These findings indicate that a significant difference exists in the taste sensitivity of salt between male and female rats. In fact, male rats that have been castrated at birth have been shown to exhibit increased salt intake throughout adulthood, whereas female rats treated with testosterone exhibit behaviors that more closely resemble the reduced appetite of normal male rats.
In one study where male and female mice were treated with furosemide and a sodium-deficient diet, male mice exhibited an increased sodium appetite as compared to females, which directly contrasts with the findings in rats. This observation emphasizes the importance of considering species-specific differences when sex differences in salt appetite are being studied.
Taken together, the activational effects of gonadal hormones like estradiol and testosterone on salt appetite remain poorly understood and require further investigation.
Salt cravings during pregnancy and lactation
Hormone levels fluctuate throughout pregnancy and likely have a direct impact on sodium intake during this time. Importantly, fetal and offspring survival is dependent upon sufficient sodium consumption by the mother during pregnancy.
In vivo studies on pregnant rats have shown that a low sodium diet leads to reduced litter sizes, live births, and offspring that survive to weaning, as well as a greater number of stillbirths. Furthermore, low sodium intake during pregnancy has been shown to alter kidney function, reduce the levels of brain proteins, as well as increase blood pressure levels of rat offspring.
In one study, non-pregnant rabbits treated with prolactin and oxytocin to mimic lactation increased their intake of sodium without causing any differences in their excretion of this mineral. This observation confirms that the increased salt appetite during lactation is also directly related to circulating hormone levels, rather than an increased loss of sodium through released breast milk.
The aforementioned mixed results on how sex hormones influence differences in salt appetite also limit the ability to conclusively determine the role of estradiol and other gonadal hormones on salt intake during gestation and lactation. Likewise, more research is needed to understand the underlying mechanisms contributing to these unique sodium intake behaviors.
Like rats, sex differences in sodium intake have also been widely reported in humans. Although sex hormones likely impact the salt appetite of many animals, such differences remain unclear in humans and are likely multifactorial.
In humans, the implications of sex differences and salt intake are often related to the health consequences of a high-salt diet. Aside from the widely known medical consequences of a high salt diet, particularly for women, its effects on reproductive health and mood are relatively unstudied.
Since salt is the only nutrient whose attraction, intake, disposition, and effects differ dramatically by sex, future research examining these differences must be conducted on female animals.
- Santollo, J., Daniels, D., Leshem, M., et al. (2023). Sex differences in salt appetite: Perspectives from animal models and human studies. Nutrients. doi:10.3390/nu15010208.