According to a study published in the journal Neurology, people diagnosed with cluster headaches are three times more likely to have other medical illnesses such as heart disease, mental disorders, and other neurologic diseases. In the study, 3,240 people with cluster headaches between the ages of 16 and 64 in Sweden were compared to 16,200 healthy cohorts with similar age, sex, and other factors.

The findings of the study showed that 92% of the people in the test group had at least one additional illness. Meanwhile, in the control group, 78%, or 12,575 people, had two or more illnesses. The researchers also found that in the test group, 96% of the women had additional illnesses compared to 90% of the men.

Additionally, they found that the average number of days a person was absent due to sickness and disability was nearly twice as high among people with cluster headaches (63 days) in comparison to those without cluster headaches (34 days). The study also suggested that people with cluster headaches and at least one additional illness had four times as many absence days compared to people with cluster headaches who did not have an additional illness. 

(Source: https://theprint.in/health/study-cluster-headache-sufferers-more-likely-to-have-other-illnesses/1266458/ )