Epidemiology and Demographics

Source: Chapter 1, section 4. Section numbering retained from the source chapter.

Who gets it, where, and how the disease is distributed — and misdiagnosed — across populations.

4. Epidemiology and Demographics

4.1 How common is it, worldwide?

The foundational meta-analysis remains:

Fischera M, Marziniak M, Gralow I, Evers S. Cephalalgia. 2008;28(6):614–618. PMID 18422717. peer-reviewed — pooled 16 population-based studies.

• Pooled lifetime prevalence: 124 per 100,000 (95% CI 101–151) — commonly rounded to “about 1 in 1,000.”
• Pooled 1-year prevalence: 53 per 100,000 (range 3–150 across the individual included studies — a very wide spread).
• Overall sex ratio 4.3:1 (M:F), with chronic CH more male-skewed (15.0:1) than episodic CH (3.8:1).
• A trend toward higher prevalence in northern vs. equatorial countries was noted but explicitly called inconclusive by the authors.
• A gap that remains unaddressed as of this research pass (2026): no population-based CH prevalence study exists anywhere in the Southern Hemisphere.

Country-level figures illustrate just how wide the spread across individual studies is:

Country / study	Prevalence (per 100,000)
Vågå, Norway (door-to-door survey, Sjaastad)	381 (highest single study)
Parma, Italy (Torelli 2005)	279
Sweden (twin registry)	151
Georgia (country)	87
Norway (national registry, Crespi 2022)	48.6
USA (AAFP estimate)	~100 (“about 1 in 1,000”)

peer-reviewed. Later, more comprehensive reviews (Kim SA, et al., Cephalalgia 2023; Membrilla JA, et al., Front Pain Res 2024, PMC10957682) largely confirm this picture without resolving the north/south or latitude question — see §4.7.

4.2 The sex ratio: a historical shift that is itself contested

The classic teaching is that CH is strongly male-predominant, historically cited at 5:1 to 6.7:1 before the 1960s. Two major studies document what looks like a steady narrowing of this ratio over subsequent decades:

Manzoni GC. Cephalalgia. 1998;18(3):138–142. PMID 9595206. peer-reviewed — 482 patients, Parma. M:F ratio by decade of onset: 6.2:1 (pre-1960) → 5.6:1 → 4.3:1 → 3.0:1 → 2.1:1 (1990s). Manzoni’s own interpretation ties this directly to lifestyle change: the female:male ratio of smoking rates in the same population fell from 8.6:1 to 1.9:1 over the same period, and the female:male employment-rate ratio moved from 2.6:1 to 1.7:1 — his argument is that changing female smoking and workforce participation, not biology, drove the apparent narrowing.

Ekbom K, et al. Cephalalgia. 2002;22(2):94–100. peer-reviewed — Swedish cohort, 554 patients. Ratio by onset decade: 5.9:1 → 5.9:1 → 3.9:1 → 3.6:1 → 3.1:1. Important nuance: the proportion of female patients did not change significantly across this period (p=0.30) — meaning some of the apparent “narrowing” may be a denominator artefact rather than a true increase in female incidence.

Explicit dissent, and arguably the single most important contested point in this entire section: the foundational Fischera et al. 2008 population-based meta-analysis (the most methodologically rigorous, least clinic-selection-biased source available) explicitly states it could not confirm the sex-ratio-narrowing trend — directly contradicting the near-universal clinic-cohort narrative found in Manzoni, Ekbom, and most 2020s review articles. This chapter treats the sex-ratio narrowing as genuinely contested, with the most population-representative source occupying the minority position, rather than presenting it as settled fact peer-reviewed.

Present-day country-by-country spread also remains wide, and shows a striking geographic/cultural pattern:

Registry/study	Country	M:F ratio
Norway national registry (2022)	Norway	1.47:1
Swedish CH biobank (Fourier 2023)	Sweden	1.9:1
Danish Cluster Headache Survey	Denmark	~2:1
UK (Bahra, May, Goadsby 2002)	UK	2.5:1
Japan (Kikui 2023)	Japan	4.5:1
China (CHRIS registry 2024)	China	4.33:1
China (Dong 2013, clinic-based)	China	7:1
Taiwan (2004)	Taiwan	6.4:1
India (2014)	India	10:1

peer-reviewed. Asian clinic-based cohorts consistently show much higher male predominance (4.3:1–10:1) than recent Northern European national registries (1.47:1–2:1) — a pattern that is not resolved in the literature reviewed: it could reflect a genuine biological/cultural difference (e.g., different female smoking prevalence or care-seeking behaviour by country), or simply different diagnostic ascertainment. Flagged as an under-discussed pattern deserving more dedicated research.

Sex ratio also varies dramatically by age of onset: from 3.3:1 in the 10–19 age bracket, up to a peak of 8.4:1 at ages 40–49, down to essential parity (1:1) by ages 60–69 — male predominance largely disappears after age 50. Proposed explanations across the sources include changing smoking/lifestyle patterns in women (Manzoni’s argument), historical underdiagnosis of women due to a “male disease” stereotype among physicians (a distinct, complementary hypothesis), general increased disease recognition over time, and speculative age-dependent hormonal factors — the last explicitly labelled “postulated” rather than established in the reviewing literature.

4.3 Age of onset

Manzoni GC, Taga A, Russo M, Torelli P. J Headache Pain. 2016;17:44. PMID 27102121. peer-reviewed — Parma Headache Centre, 808 patients.

• Mean age of onset: 30.2 ± 13.8 years (men 30.1 ± 13.0; women 30.4 ± 15.7) — essentially identical between sexes on average, with a peak in the third decade of life for both.
• Women with primary chronic CH had markedly later onset (mean 42.8 ± 21.7 years) than women with episodic CH.
• A bimodal onset pattern specific to women with chronic CH was found: peaks in the 2nd and 6th decades of life; men with chronic CH showed a milder bimodality (3rd and 5th decades).
• At the onset-age extremes (≤15 years or ≥50 years), the usual male preponderance was actually inverted — more women than men.

Ekbom’s Swedish cohort similarly found a possible second onset peak in women with episodic CH in their 50s, “with a number of sufferers having their first attacks after the menopause” peer-reviewed. A distinctly different pattern was found in one Japanese study cited by Kim et al. (2023, Cephalalgia): men peaking in their 20s–30s, but women peaking in their 10s and 60s — a different bimodal shape from the Western (Manzoni) pattern peer-reviewed.

National variation in mean onset age:

Country	Mean age of onset
France	33.9 ± 14.7
Norway	32.5 ± 13.4
Sweden	31.9 ± 13.6
Germany	31.6 ± 12.0
Denmark	31.6 ± 13.7
Netherlands	31.1 ± 13.0
Japan	31.0 ± 13.8
Italy	30.3 ± 14.0
Taiwan	27.2 ± 12.1
China (Dong 2013)	26.7 ± 10.9
China (CHRIS 2024)	24.9 ± 9.8 (women significantly younger: 23.1 vs. men 25.3, p=0.011)

[PEER-REVIEWED, tabulated from Kim et al. 2023 review and national cohorts]. East Asian cohorts trend toward a slightly younger mean onset (~25–27 years) than European cohorts (~31–34 years) — flagged as a pattern, not a settled causal finding, since it could reflect differing registry-entry ages rather than a true biological difference.

4.4 Smoking: a strong correlation with a genuinely paradoxical causality story

Prevalence: smoking rates among CH patients are strikingly high and consistent across independent countries:

• USA (Rozen & Fishman, 2012, n=1,134): 77% smokers.
• Italy (Rossi et al., n=200): 81% ever-smokers (“up to 90% of males, ~70% of females”).
• Denmark (Lund et al. 2019, case-control, n=400 vs. 200 controls): 48.3% current smokers vs. 9.0% of controls (p<0.001); 74.5% ever-smokers vs. 30.0% of controls.
• South Korea (Chung et al., KCHR, n=250): 60.8% ever-smokers; strikingly sex-differentiated — 70.3% of male patients vs. only 12.2% of female patients.
• Kuwait (Al-Hashel et al., n=172): 83.7% smokers.
• Pooled meta-analytic estimate (2025 systematic review, PMC12139338): 65% (95% CI 55–76) weighted current-smoking prevalence in CH, vs. 19% in tension-type headache.

All peer-reviewed.

The causality paradox — presented here explicitly, not smoothed over:

Evidence for causality: the Winsvold 2023 GWAS (§3.6) found Mendelian randomisation evidence that smoking intensity has a causal effect on CH risk (genetic-causality proportion >0.6, p=8.57×10⁻¹⁰).

Evidence against simple causality: multiple independent clinical studies find that quitting smoking essentially never improves established CH:

• Rossi et al. (Italy): only 23.8% of former smokers reported any reduction in active-phase length after quitting; 66.7% reported no change; average time since quitting was ~8 years (ample washout time).
• Rozen & Fishman (US): of smokers who quit specifically to try to improve their CH, only 3% experienced relief.
• Danish Cluster Headache Survey (Lund et al. 2019): explicitly states “smoking cessation has not been found to improve CH… and not all smokers develop [CH]” — arguing smoking is neither necessary nor sufficient.
• Korean cohort: the latency between starting smoking and CH onset (mean 15.6–15.9 years across Korean and Danish cohorts) was judged “too long to suspect a direct causal relationship” in the classic sense.

How the sources attempt to reconcile this: the leading hypothesis is that smoking (including secondhand/parental exposure in childhood — one analysis found a 2.5-times increased risk of earlier-onset CH with childhood secondhand exposure) may act as an early-life triggering exposure that permanently alters CH liability, such that once the disease is “switched on,” removing the trigger does not reverse it. An alternative explanation is that smoking and CH share common underlying genetic/behavioural vulnerability (impulsivity, risk-taking, ADHD-linked traits — all genetically correlated with CH in the Winsvold GWAS) rather than one directly causing the other. Neither explanation is proven; this is presented as an open question, and a 2025 meta-analysis (PMC12139338) adds a further wrinkle by finding no significant association between current smoking and CH in its own pooled odds-ratio analysis — despite the ~65% raw prevalence — directly in tension with the Danish case-control data’s highly significant finding. This discrepancy is flagged as genuinely unresolved, possibly due to different control-group definitions across the pooled studies peer-reviewed.

4.5 Geography, latitude, and seasonality

• Fischera et al. (2008) noted a trend toward higher prevalence in northern countries but called it inconclusive, given the near-total absence of Southern Hemisphere data.
• A dedicated 2024 review (Curr Pain Headache Rep, PMID 38441794) peer-reviewed — the first systematic literature review specifically testing the latitude hypothesis — found positive associations between latitude and: 1-year prevalence, proportion of chronic (vs. episodic) CH, and proportion of cranial autonomic signs (miosis/ptosis). It concluded latitude “may affect the phenotypic presentations of cluster headache, probably partially mediated via temperature and sunlight variations” — directly in tension with Fischera’s earlier “independent of region” conclusion. Presented here as unresolved.
• Seasonality: circannual peaks cluster in spring and autumn (accounting for 53.8% of reported onset timing across studies), most pronounced at higher latitudes (Denmark, Sweden, Norway, Italy, northeastern USA, northern China) where seasonal daylight variation is more pronounced. Lower-latitude regions show genuinely different seasonal phenotypes: India reported peaks in summer (30%) and winter (16%); the southwestern USA (California, Kudrow 1984 cohort) reported peaks in January and July rather than the spring/autumn pattern. This latitude-dependent seasonal shift is a real, specific, and likely under-appreciated finding.

4.6 East Asia as a distinct epidemiological cluster

A consistent, independently cross-replicated pattern across Japanese, Chinese, and Taiwanese cohorts sets East Asian CH populations apart from Western ones in at least four ways:

1. Much lower proportion of chronic (vs. episodic) CH: Japan (Kikui 2023) 4.5%; Japan (Ogawa 2011) 3.5%; China (Dong 2013) 7.5%; China (CHRIS 2024) 2.33% — versus 10–37% typically reported in Western cohorts.
2. Higher male predominance (4.3:1–7:1) than recent Northern European registries (1.5:1–2:1) — see §4.2 table.
3. A distinctive “uncoupling” of subjective restlessness from overt restless behaviour during attacks, specifically documented in Japanese and Taiwanese patients (§2.3).
4. Broadly similar, if not longer, diagnostic delays to Western countries despite very different healthcare systems (§4.7) — e.g., China’s CHRIS registry found 39.22% of patients experienced a 10-year-plus diagnostic delay.

There is also a genuinely notable finding within the Chinese CHRIS registry (Zhang S, et al., Cephalalgia 2024, PMID 38501875, n=816, the first large multicentre national CH registry in China) peer-reviewed: women had significantly earlier onset than men (23.1 vs. 25.3 years, p=0.011) — the opposite direction to some Western later-onset-in-women findings, and worth flagging as its own distinct, possibly under-highlighted result. The same registry found only 35.67% of patients received guideline-recommended acute treatment and 24.26% preventive treatment, indicating substantial undertreatment alongside diagnostic delay.

Explicit gap: no true general-population epidemiological prevalence study exists for CH in Japan as of the most recent review located — only small clinic- or claims-based samples. No equivalent of the Danish/Dutch/Italian national registries exists for South America, Africa (beyond a single small Ethiopian clinic sample), or Oceania.

4.7 Diagnostic delay: a real, shrinking, but still substantial problem

The most authoritative pooled figure:

“Cluster headache diagnostic delay and its predictors.” PMC11980061 (2025 meta-analysis). peer-reviewed — overall pooled diagnostic delay: 10.43 years (95% CI 9.09–11.77).

Country-level mean delays vary considerably: UK 2.6 years; Flanders (Belgium) 3.6 years; Spain 4.9 years; Italy/Eastern Europe 5.3±6.4 years; Denmark 6.2–9 years (two studies); USA 6.6–8.5 years; Japan 7.3±6.9 years; Serbia 7.8±8 years. In one US study, 42% of patients waited more than 5 years for a correct diagnosis. Migraine, trigeminal neuralgia, sinusitis, and dental/jaw disease are the most consistently cited misdiagnoses — a meaningful minority of patients undergo unnecessary sinus surgery, dental extractions, or septum surgery before correct diagnosis (one Italian hospital-based study found 93% underwent instrumental/laboratory investigations before correct diagnosis, and 4% of a US survey sample had unnecessary sinus or deviated-septum surgery). (Editor’s note: a fuller country-by-country table of diagnostic delay, including within-country discrepancies, is in Part IV, §3.)

The good news, clearly documented across multiple independent national datasets: diagnostic delay has been shrinking substantially decade over decade, especially since 2000. The Danish Cluster Headache Survey shows this most clearly:

Decade of onset	Mean diagnostic delay (years)
1950s	39.0
1960s	25.1
1970s	20.8
1980s	12.1
1990s	6.6
2000s	3.9
2010s	0.9

peer-reviewed. A Greek study found an even starker version of the same trend: patients with onset before 2000 waited a median of 13 years, versus a median of 1 year for onset after 2010.

Predictors of longer delay appearing consistently across independent studies: younger age at onset (age <20 at onset → 13.8 years delay in the Danish cohort, vs. 2.1 years for onset after age 40); attack duration >180 minutes; migraine-like features; nocturnal attacks.

A subtle but important point that should not be collapsed into a simpler claim: despite a strong general narrative that women are underdiagnosed relative to men, the most rigorous primary studies that directly tested this (Danish 2020 cohort study; Dutch 2003 nationwide survey; the 2025 meta-analysis of predictors) consistently found no significant independent association between female sex and diagnostic delay duration. However, some of the same cohorts did find women were more frequently misdiagnosed at some point in their diagnostic journey (Danish data: 61% of women vs. 46% of men were misdiagnosed at some stage, even though the average delay length did not differ significantly by sex). These are two different claims — “takes longer to diagnose” vs. “more often misdiagnosed along the way” — and the evidence supports the second more clearly than the first peer-reviewed.

4.8 Comorbidities and suicidality: another genuinely contested area

• Rozen & Fishman (2012, US survey, n=1,134): 55% reported suicidal ideation. peer-reviewed
• Karolinska Institutet Swedish survey (n=500): more than 50% reported suicidal ideation (vs. ~9% in the Swedish general population); more than 50% reported self-harm behaviour during attacks (vs. ~5–17% in the general population). peer-reviewed
• Lee MJ, et al. Cephalalgia. 2019;39(10):1249–1256. peer-reviewed — Korean registry, 175 patients in-bout: during attacks, passive suicidal ideation 64.2%, active ideation 35.8%, suicidal planning 5.8%, suicide attempt 2.3%; interictally (still in-bout but between attacks) these figures dropped sharply (4.0%, 3.5%, 2.9%, 1.2%); during remission, near zero. This strongly suggests suicidality in CH is largely state-dependent, tightly tied to active attacks rather than a constant background trait.
• The most recent and largest formal meta-analysis (PMC12676835, late 2025) peer-reviewed found a much lower overall pooled rate: suicidal ideation 8.0% (95% CI 7.7–8.3), suicide attempts 1.2% (95% CI 1.1–1.3) — but in specialised clinical/patient-organisation settings specifically (the kind of sample most other studies here draw from), ideation rose to 44.6% and attempts to 5.1%. The authors’ own conclusion: “the overall suicidal risk in CH does not appear to be higher than that of the general population, but there is a suicidal risk increase among CH patients followed up in specialized field[s]” — i.e., much of the widely-quoted ~50%+ figures likely reflect sample selection bias toward more severely affected, treatment-seeking patients, not the average person with CH.
• In apparent tension with this more reassuring population-level conclusion: a large Danish national registry study (JAMA Neurology, 2025, n=119,486 headache-diagnosed individuals including 6,872 with trigeminal autonomic cephalalgias) found headache diagnoses broadly are associated with meaningfully elevated suicide risk at a true population level (TAC diagnosis: adjusted hazard ratio 1.97 for suicide attempt, 2.40 for completion, versus matched controls). This study’s TAC category is not CH-specific, so it is suggestive context rather than a CH-specific figure — but it sits in real tension with the CH-specific meta-analysis’s more cautious conclusion, and this chapter presents both rather than picking a winner peer-reviewed.

Broader comorbidity profile (Norway national registry, Crespi et al. 2022, the most methodologically rigorous true-population-level comorbidity study available, n=1,891 CH patients among 3,892,260 adults) peer-reviewed: significantly elevated, age/sex-adjusted odds ratios for medication-overuse headache (OR 50.7), migraine (OR 25.2), chronic post-traumatic headache (OR 22.2), somatoform disorders (OR 4.2), suicide attempt (OR 3.9), personality disorder (OR 3.6), bipolar disorder (OR 3.6), depression (OR 2.8), substance abuse (OR 2.6), and cerebrovascular disease (OR 2.4).

Familial CH and demographics (Russo, Manzoni, Taga, et al., Parma, PMID 26017530, n=785 probands) peer-reviewed: positive family history in 5.1% of probands; M:F ratio lower among familial cases (2.3:1) than non-familial cases (2.7:1); women with familial CH had significantly younger onset (28.5 years) than women with non-familial CH (46.7 years, p<0.01) — no such difference in men, suggesting a possible sex-specific genetic effect on both onset age and sex ratio within familial CH specifically.

Compiled from PubMed/PMC, ICHD-3 official classification text, the journals Cephalalgia, Headache, The Lancet, Pain, Annals of Neurology, and JAMA Neurology, the Danish Headache Center (Rigshospitalet), Clusterbusters.org, OUCH(UK), Reddit r/clusterheads and r/ClusterHeadaches, and German, Danish, Italian, Japanese, and Chinese-language clinical literature and patient communities. Four detailed research memos (history, clinical picture, mechanism/pathophysiology, epidemiology) underpin this chapter; full source lists with URLs are preserved in the underlying research files for follow-up verification.