With all the talk about the risks of "polypharmacy" - being prescribed more than five medications - it might be surprising to learn that not receiving enough of the right prescriptions can also significantly increase your risk of being hospitalized or dying.

Yet that is exactly what a new study from Belgium finds.

"Absence of polypharmacy is not a simple indicator of quality of care," Dr. Maarten Wauters from Ghent University told Reuters Health. "Patients with just a few medications could be at risk of missing essential and beneficial medications."

Wauters' team looked for possible links between prescriptions and hospitalizations and death in their study of 503 people aged 80 years and older who were living at home.

Unlike earlier studies that focused on polypharmacy, the researchers also studied medication underuse (not having a prescription for a medical condition) and misuse (receiving an inappropriate prescription or not using it optimally).

More than half of the study participants were taking five or more medications, but still, two-thirds were not receiving medications they should have, and 56 percent were misusing medications. Four out of 10 patients were both underusing and misusing medications.

"Only in 9 percent of this population, no polypharmacy, no underuse, and no misuse was observed," Wauters said by email.

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The most common health problems participants had were high blood pressure, osteoarthritis and high cholesterol. Drugs for heart problems, blood thinning and nervous system problems were the most commonly taken.

During the 18 months covered by the study, 9 percent of individuals died and 31 percent had to be hospitalized.

The risk of death increased by 39 percent for each additional prescription an individual should have received but didn't, and the risk of hospitalization increased by 26 percent for each underused prescription.

Individuals who didn't receive three or more medications they should have were almost three times as likely to die and twice as likely to be hospitalized as those who received all of the appropriate medications.

The most commonly underused drugs were so-called ACE inhibitors for people with heart failure, and blood thinners and statins for people with documented heart or vascular disease. These were followed by inhalers for asthma or COPD and vitamin D or calcium for people with osteoporosis.

The most commonly misused drugs were benzodiazepines, tranquilizers that should not be taken for more than four weeks. These were followed by duplicated drugs, such as two similar pain killers, two medications for blood thinning or two antidepressants from the class known as SSRIs.

After accounting for the number of medications people were taking and underuse, misuse was not associated with the risk of dying or being hospitalized, according to the results in British Journal of Clinical Pharmacology.

"It has been proven that regular medication evaluations can help prescribers and their patients to keep the medication therapy optimal," Wauters said. "Patients need to question their medications as well: 'Is it really necessary to take these sleeping pills? Do I need something for this new disease I have? Do I have to take this pill, even if I don't feel any changes?'"

Wauters added that physicians and patients need to work together to find the best combination of medications to treat their unique mix of medical conditions.