The kidneys clean the blood by removing waste products, form urine and regulate urine’s salinity, acidity and volume. The kidneys also have other functions in the body and are also closely linked to blood-pressure regulation, fluid balance and the production of red blood cells. A failing kidney is also less efficient at producing the active form of vitamin D that is important for the absorption of calcium in the intestine. Even other biomarkers linked to the skeleton, such as parathormone and phosphate, are affected by impaired kidney function, something that in the long term may lead to skeletal fragility. Osteoporosis afflicts women more often than it does men and leads to an increased risk of fractures. Just over half of all women over 80 suffer from osteoporosis.
“As disease is often defined as a loss of function in an organ, it can sometimes be difficult to distinguish disease from normal aging. In the case of kidney function in the elderly, the picture may become even more complicated as there are many different formulas for estimating kidney function, most of which have not been developed for older people. This despite the fact that it is elderly patients who consume most healthcare,” says Linnea Malmgren, doctoral student at Lund University and resident physician at Skåne University Hospital in Malmö, who has recently defended her dissertation, Kidney Function During Ageing and its Association with Bone Mass, Fracture and Mortality.
Kidney function differs between young and elderly people; kidney function that would be considered impaired in a young individual need not be linked to a chronic disease in an elderly individual – it may simply be a function of normal aging. Kidney failure is a silent disease and the individual does not notice that their kidney function is declining. By the time symptoms such as fatigue, itching and nausea become apparent, the situation will generally be far gone.
In her doctoral project, Linnea Malmgren studied how kidney function in the elderly is linked to bone mass and fractures. The dissertation is based on four epidemiological studies and follows a total of 1,044 elderly women in the cohort Malmö Osteoporosis Prospective Risk Assessment (OPRA) for over a decade. The studies are based on data collected between 1995 and 2012, from when the women reached 75 years of age and with follow-ups at 80 and 85 years.
The overall results of the dissertation demonstrate that, according to the current system for assessing kidney function, chronic kidney disease was very common among the otherwise healthy women. Among the oldest women, eight out of ten were classed as having kidney disease depending on which measurement method was used.
“Among other things, kidney function in an individual varies due to diet and the time of day and is affected by risk factors such as smoking and high blood pressure. Not only that but the markers for impaired kidney function, cystatin C and creatine, are affected by functions other than the kidneys’ own,” says Linnea Malmgren.
According to the current system for assessing kidney function, a large proportion of the elderly women in the study are classified as having kidney disease; however, only in those women with the very worst kidney function did the risk of death increase by two to three times compared to women with health kidneys. Linnea Malmgren therefore believes that the threshold for kidney disease should be lowered for older individuals and that further studies of the elderly and comorbidity are required. Osteoporosis and kidney failure affect quality of life for the individual patient and demand expensive healthcare and social investments.
“Demographics are constantly changing and the number of people of 80 years or over is expected to increase by almost 80% by 2035. In healthcare we already need increased knowledge about preventative measures to prolong healthy aging and prevent future hospitalisations,” says Linnea Malmgren.