Increased phosphate intake elevates blood pressure in healthy adults

They make processed cheese spreadable, prevent coffee from clumping and help preserve many meat products: phosphates are a common additive in industrially produced foodstuffs.

Natural foods also contain phosphates, but modern eating habits mean that we are increasing our intake of them. Increased consumption of processed foodstuffs has significantly increased phosphate intake in recent years, which now often exceeds the daily intake of 700 mg recommended in the US.

Healthy people also at risk

As a high phosphate level can lead, for example, to deposits in blood vessels, a low-phosphate diet has long been recommended for people with chronic kidney problems.

However, an increase in dietary phosphate also increases the likelihood of developing or even dying from arteriosclerosis or a cardiovascular disease in healthy people. This has been shown by epidemiological studies that examine the connection between potential risk factors and certain diseases.

Physiological study with young adults

For the first time, a research team led by Professor Reto Krapf from the University of Basel has now verified this statistical connection in a qualitative study with 20 healthy test subjects.

Over 11 weeks, half of the participants received an additional dose of sodium phosphate in tablet form alongside their normal diet. This increased the phosphate content in their blood to an above-average level, albeit one that is widespread in the population.

The second group took a phosphate binder that inhibits the substance's intake in the body. They also received salt as sodium chloride to equal the first group's sodium intake.

Effect on blood pressure and pulse rate

After six weeks, the doctors examined the effects of the different diets on various cardiovascular indicators such as blood pressure and pulse. A comparison of the two groups showed that the increased phosphate intake significantly increased the systolic and diastolic blood pressure of healthy young adults -- by 4.1 and 3.2 mmHg, respectively. At the same time, pulse rate increased by an average of four beats per minute.

The researchers show that increased phosphate intake, more specifically an increased serum phosphate level, activates the sympathetic nervous system, which accelerates cardiac activity and increases blood pressure. The study demonstrated the effect to be reversible: two months after the end of the study, the participants' levels had returned to normal.

No effect of vitamin D

Vitamin D is increasingly prescribed for various reasons. It both stimulates intestinal phosphate absorption thus further increasing phosphate load, but also as putative cardioprotective effects. Therefore, in the second phase of this study, the effect of an additional supplement of vitamin D was examined. However, no measurable influence on the cardiovascular values was found in either group.

"Our results provide an important explanation for the association of dietary phosphate intake with increased cardiovascular morbidity and mortality in the general population," says study leader Reto Krapf. "These conclusions are important for public health and should be further examined in larger studies in various population groups."

The study was supported by the National Center of Competence in Research (NCCR) Kidney Control of Homeostasis.