Table 3

Summary of studies reviewing environmental factors in the onset of GCA

Environmental RF	Country	Years	Cases	Diagnosis	Outcome summary	Significant	Author
Seasons and annual cyclic trends
Seasons	Australia	1992–2011	314	TAB	Summer (January/December) month increased incidence (p=0.015)	Yes	Dunstan et al 37
Seasons and infection	Denmark	1982–1994	–	TAB and clinical	Quarterly and annual fluctuations seen (association with infectious epidemics)	Yes	Elling et al 10
Seasons	France	1983–1995	109	TAB and clinical	No seasonal variation but peak in December	No	Ramassamy et al 40
Seasons	France	1993	213	–	No seasonal pattern	No	Raynauld et al 41
Seasons	Israel	1980–2004	210	TAB and ACR	Incidence more common late spring/early summer (p<0.001)	Yes	Bas-Lando et al 9
Seasons	Israel	1980–1991	84	TAB	Incidence more common during May to June (p<0.0005)	Yes	Sonnenblick et al 20
Seasons	NZ	1996–2005	70	TAB	Incidence greatest in spring (p<0.9)	No	Abdul-Rahman et al 8
Seasons	Spain	1981–2005	255	TAB	No seasonal pattern over 25 years	No	Gonzalez-Gay et al 33
Seasons	Spain	1976–2001	184	TAB and clinical	No cyclic or seasonal pattern of variation	No	Liozon et al 39
Seasons and cycles	Spain	1981–1999	161	TAB	No seasonal or annual incidence pattern seen in the Lugo region	No	Gonzalez-Gay et al 42
Season	Spain	1985–1997	143	–	No seasonal variation	No	Narváez et al 43
Seasons	Sweden	1997–2010	840	TAB	No seasonal or significant monthly variation	No	Mohammad et al 44
Seasons and cycles	Sweden	1976–1995	665	TAB	Random annual trends. Season predominance in winter and autumn (p=0.041)	Yes	Petursdottir et al 18
Seasons and cycles	USA	1994–2011	215	TAB	No significant fluctuations in the annual or monthly data (p=0.55).	No	Kisza et al 45
Seasons and cycles	USA	1950–1999	173	TAB and ACR	Cyclic incidence peaks 7–10 yearly, last ~3 years. No significant seasonal pattern	No	Salvarani et al 46
Latitude
Latitude	Norway	1992–1996	70	TAB and ACR	No incidence difference between Northern and Southern Norway	No	Haugeberg et al 21
Latitude (and seasons)	UK	1990–2001	3928	Clinical (GPRD)	Incidence in South-North (UK), and greater in summer months (p=0.0022)	Yes	Smeeth et al 13
Altitude
Altitude	Spain	1981–2001	–	TAB	Altitude had no effect on incidence of GCA (altitude ranged from 100 to 952 m)	No	Llorca et al 23
Solar cycle and sunlight
Solar and geomagnetic	USA	1950–2004	–	–	Geomagnetic activity may explain temporal variation and east-west skewness	Yes	Wing et al 26
Solar exposure	Australia	1997	2	Skin biopsy	Solar aetiology: link between actinic granulomas and GCA of subcutaneous vessels	–	Lau et al 47
Solar exposure	Australia	1987	4*	Clinical and TAB	Observations: actinic radiation=vascular risk factor (elastotic/lytic properties)	–	O’Brien48
Solar exposure	UK	1965	60	Clinical	Sun exposure may cause GCA (14/18 cases sun exposed). Incidence up in June	–	Kinmont and McCallum19
SES
Occupation and SES	Sweden	1964–2008	8019	Hospital register	Education, marital status, SES, occupation only weakly associated with GCA	No	Zöller et al 22
SES	UK	2005–2009	271	TAB and ACR	Area-level socioeconomic deprivation associated with ischaemia from GCA.	Yes	Mackie et al 29
SES, sunlight, infection	France	1970–1979	94	–	Environmental factors (sun exposure, lifestyle, SES) do not affect incidence	No	Barrier et al 49
Urban versus rural
Urban versus rural	Germany	1994	79	ACR	GCA was more common in the urban than in the rural populations	Yes	Reinhold-Keller et al 30

Symbol (–) denotes unable to complete this information.
*Observational study with numbers not well defined.
ACR, American College of Rheumatology; GCA, giant cell arteritis; GPRD, General Practice Research Database; NZ, New Zealand; RF, risk factors; SES, socioeconomic status; TAB, temporal artery biopsy.