Excess consumption of phosphate over-activates nerves that raise blood pressure, leading to abnormally high blood pressure, a new study in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology reports. Phosphate is commonly used in foods as a preservative, flavor enhancer and color stabilizer. The findings highlight the need for further studies in humans to determine if the amount of added phosphate should be included on food labels.
The brain controls bodily processes by balancing the activity of two sets of nerves: sympathetic and parasympathetic. Sympathetic nerves prepare the body to handle stressful situations, such as exercise, while parasympathetic nerves maintain the body during rest. Blood pressure changes as a result: Activating sympathetic nerves raises blood pressure, while activating parasympathetic nerves lowers blood pressure. Overactive sympathetic nerves are a significant contributor to the development of hypertension, or constantly high blood pressure.
Phosphate is naturally found in meat and milk and is important for building strong bones and maintaining and repairing the body. However, because phosphate is added to a large number of packaged foods, the typical American diet contains twice the daily recommended allowance, says Wanpen Vongpatanasin, MD, of University of Texas Southwestern Medical Center and co-lead investigator of the study. Earlier studies in patients and rats have suggested that consuming too much dietary phosphate can lead to hypertension and other cardiovascular complications. This new study investigated the involvement of the sympathetic nerves by examining the nerves' activity when resting and exercising.
Rats ate a diet containing twice the amount of phosphate optimal for rodents for three months. The research team found that rats on a high-phosphate diet had higher resting blood pressure and exaggerated increases in sympathetic nerve activity and blood pressure during exercise.
While blood pressure normally rises during exercise, too much of an increase increases the risk of heart attack, stroke and unhealthy thickening of the heart's walls, Vongpatanasin says. In addition, because exercise is commonly recommended to control high blood pressure, an excessive blood pressure increase would limit the possibility of exercise as a hypertension therapy, says Scott Smith, PhD, of University of Texas Southwestern Medical Center and co-lead investigator of this study.
"Our findings may have relevance in terms of raising safety concerns regarding long-term consequences of phosphate additives in our diet," according to Vongpatanasin. Population studies should be conducted to confirm the study, Vongpatanasin says. If consistent, the findings would support including the amount of added phosphate in food labeling. "As with sodium, such a revision would not only allow the American public to monitor their phosphate intake but also serve as a warning that their health could be compromised by excess consumption of phosphate," the authors wrote.
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