Table 2. Cumulative incidence of ulcer from birth and during the 4-year follow-up period, Japan Nurses’ Health Study, 2001–2013.

ABO blood type	From birth (n = 1,336)			Four-year follow-up (n = 202)
	Number of Cases	Cumulative Incidence %	95% CI	Number of Cases	Cumulative Incidence %	95% CI
O	428	10.9	9.9–11.9	58	1.5	1.1–1.9
Non-O	908	9.6	9.0–10.2	144	1.5	1.3–1.8
A	500	9.7	8.9–10.5	86	1.7	1.3–2.1
B	275	9.1	8.1–10.2	34	1.1	0.8–1.6
AB	133	10.3	8.7–12.1	24	1.9	1.2–2.8
By birth year
Pre-1956
O	176	15.5	13.4–17.7	19	1.7	1.0–2.6
Non-O	366	13.2	11.9–14.5	47	1.7	1.2–2.2
A	197	13.2	11.6–15.1	29	2.0	1.3–2.8
B	115	12.7	10.6–15.1	12	1.3	0.7–2.3
AB	54	13.9	10.6–17.8	6	1.6	0.6–3.3
Post-1955
O	252	9.0	8.0–10.1	39	1.4	1.0–1.9
Non-O	542	8.1	7.5–8.8	97	1.5	1.1–1.8
A	303	8.2	7.4–9.2	57	1.6	1.2–2.0
B	160	7.6	6.5–8.8	22	1.0	0.7–1.6
AB	79	8.7	7.0–10.8	18	2.0	1.2–3.1

CI, confidence interval; Non-O, A, B, and AB blood groups.