Patients with low levels (below 0.75 (millimoles/litre (mmol/L)) of phosphate in their blood were at a similar risk of cardiac events as those with elevated levels (above 1.5 mmol/L), reported the researchers from the University of Surrey.
The team found approximately a 75% increase in risk of heart attack, acute coronary syndrome or revascularisation procedure in those with either low or excessive blood phosphate concentrations, compared with patients with mid-range (1-1.25 mmol/L) levels.
Previous research had already shown links between high blood phosphate content and cardiac health risk. However, this is the first study to identify the potential dangers of inadequate levels.
The researchers therefore proposed a U-shaped risk curve, and suggested that the definition of ‘normal’ phosphate level may need to be re-examined.
“The extremes of serum phosphate may confer cardiac event risk with a U-shaped trend. In particular, we raise new cardiac concerns for low serum phosphate in the general population. Also, the normal range for phosphate may require redefinition among healthy adults,” wrote lead author Dr. Nick Hayward.
"Our findings shed new light on the role of phosphate in the body and its relationship to cardiovascular health," commented co-author Dr Andy McGovern. “In light of our findings we would suggest that clinicians consider people with low phosphate levels to be at higher cardiovascular risk and assess ways in which this can be reduced for each patient."
Phosphorous can be found in protein-rich foods including meat, poultry and fish and is known to have many biochemical roles including signal transduction, mineral metabolism and energy exchange.
The study was a retrospective cohort study which used data extracted from the Royal College of General Practitioners—Research and Surveillance Centre (RCGP-RSC) database. The researchers looked at the serum phosphate levels of more than 100,000 patients aged 18-90 and correlated them with cardiac events over five- and nine-year periods. The scientists used the mean of up to five phosphate measurements prior to any cardiac event.
The findings came as somewhat of a surprise to the researchers, as previous research had suggested low serum phosphate as cardio-protective. Replication of the results are therefore necessary, the researchers advocated.
“We conclude that this novel association warrants further validation in other large-scale cohort studies,” wrote Hayward.
"The importance of phosphate in primary and secondary healthcare should be reviewed. It is often overlooked in blood tests yet phosphate may be a new risk factor for heart disease in adults,” he added.
Source: PLOS ONE
Published online 8th November 2017, doi: 10.1371/journal.pone.0184774
“U-shaped relationship between serum phosphate and cardiovascular risk: A retrospective cohort study”
Authors: Nicholas Hayward, Andrew McGovern, Simon de Lusignan, Nicholas Cole, William Hinton, Simon Jones