Phosphorus: A Necessary Evil
Phosphorus is necessary for life. Our cells store energy with it, wrap themselves with it, and make genes with it. Consequences of low phosphorus intake occur with severe starvation and disorders of phosphorus transport in the body. Phosphorus excess presents more of a problem.
In my world of kidneys (or lack thereof), excess phosphorus does a number of evil things. As its blood levels rise, it can stimulate secondary hyperparathyroidism and renal osteodystrophy. It can also precipitate with calcium in tissues causing a number of issues. Calcification in coronary arteries indicates atherosclerosis, with significant risk of heart attack and death. Cardiovascular disease is what kills most people with kidney failure. Blood phosphorus levels run higher in patients of lower socioeconomic status, probably because of reliance on inexpensive processed foods that contain phosphate additives readily absorbed by the gut.
Higher baseline phosphorus levels have been shown to associate with greater risk of cardiovascular disease 15 years later in young adults with normal kidney function. In these patients, levels remained within the normal range- not the elevated levels seen in kidney disease patients. So even high normal levels of phosphorus can be bad for you.
The article by Brendan Borrell looks at the work of two very different scientists. James Elser, a limnologist, was interested in why phosphate loading produces accelerated growth of certain organisms in lakes. His research group found that the increased phosphorus could be explained by the rapid production of RNA by briskly reproducing organisms. Phosphorus seemed to be the “rate-limiting” substance for growth. Molecular biologist George Beck studies carcinogenesis and the role of signaling driven by extracellular phosphate in it. While his own experiments suggest that dietary phosphate may drive cancers, other studies are less supportive. Atherosclerotic lesions may include areas of inappropriate cell growth; thus, phosphorus may first trigger vessel wall damage (intimal hyperplasia, or excessive growth of cells lining the blood vessel) which then becomes a target for precipitation of calcium phosphate.
So what should people do? Major sources of dietary phosphorus include meat and milk. Fast-food and highly processed products also contain phosphates that may be the difference between health and disease (Davita has a nice post on hidden phosphorus in foods). Given the link between these food sources and other health problems, such as obesity, hypertension, and diabetes, limiting their consumption seems prudent.