Women, on average, tend to receive diagnoses for various diseases years later in life than men do, according to an extensive new studythis link opens in a new tab out of Denmark.

The study, based on the population-wide Danish National Patient Registry, analyzed data from 6.9 million hospitalized patients over a 21-year period, and found that women were diagnosed, on average, four years later than men in connection with 770 types of diseases, according to Science Dailythis link opens in a new tab.

“(This) actually surprised us quite a lot,” lead author Søren Brunak told Reuters Healththis link opens in a new tab. “Men generally have a tendency to get to the doctor later… So presumably the difference in onset is even larger.”

The study looked at various diseases specifically, and found that women were 2.5 years older than men when they received cancer diagnoses, and 4.5 years older when it came to metabolic diseases like diabetes.

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An average of six years between men and women was found in connection with ADHD; boys were, on average, 14 years old when they were diagnosed, and women were 20. According to Science Daily, however, the researchers note that the age discrepancy could be because women have a different subtype of ADHD which results in more mild-mannered behavior than seen in boys with ADHD.

One disease noted as the exception is osteoporosis – the study found that women were typically diagnosed before men when it came to the bone condition.

Science Daily notes that scientists are still unsure as to whether the diagnosis delays are due to genetics, environment, diagnostic criteria or some type of combination, and are investigating causes in collaboration with a research team from Finland.

The study was published in the scientific journal Nature Communications with research from the Norvo Nordisk Foundation's Center for Protein Research, the Faculty of Health and Medical Sciences at the University of Copenhagen.