Table 1.

Demographic details of the twins studied

	Monozygotic twins (n=1856)	Dizygotic twins (n=2064)	p Value
Age (y)	51 (19–81)*	52 (20–82)*	0.13
Female	91%	93%	0.05
At least weekly GORD symptoms	18%	18%	0.98
Body mass index (kg/m2)	25 (14–47)*	25 (15–54)*	0.01
Ever smoked	36%	45%	<0.01
Excess alcohol†	5%	6%	0.54
Anticholinergic drug therapy	7%	6%	0.18
Oral contraceptive or HRT	24%	26%	0.17
Parental family history of upper GI disease	26%	24%	0.15
Right handed	88%	88%	0.92

p values are corrected for relatedness of the twins.

*Mean (range).

†Excess alcohol intake defined as >28 units per week for a man and >21 units per week for a woman.

GORD, gastro-oesophageal reflux disease; HRT, hormone replacement therapy; GI, gastrointestinal.