Table 1. Subgroup analyses per 1% increment^a of blood DHA^b concentration and risk of PCa.

Subgroup factor	Number of studies	Relative risk (95% CI)	Heterogeneity within sub-group		Heterogeneity between sub-groups	Nonlinearity
			I2	Degree	P value	P value
Overall analysis	9	1.02 (1.00, 1.05)	26.2%		—	0.11
Study design
Nested case-control	7	1.02 (0.99, 1.05)	17%	Low	0.61	0.09
Case-cohort	2	—	—		—	—
Grade or stage of cancer
Aggressive	5	1.08 (0.99, 1.18)	84%	High	—	0.83
Non-aggressive	4		—	—	—	<0.01
Follow-up duration
≤7.4 years	6	1.03 (1.00, 1.06)	25%	Low	0.08	0.88
>7.4 years	3	—	—	—		0.04
Regions
USA	5	1.02 (0.99, 1.06)	38%	Moderate	0.64	0.99
European countries	3	—	—	—		0.02
Australia	1	—	—	—	—	—
Covariate adjustment
Adjusted for age	5	1.02 (0.99, 1.06)	38%	Moderate	0.98	0.99
Not adjusted for age	4	1.01 (0.97, 1.06)	33%	Moderate		0.36
Adjusted for BMI	4	1.03 (1.00, 1.05)	0%	Low	0.61	0.41
Not adjusted for BMI	5	1.00 (0.94, 1.07)	53%	Moderate		0.31
Adjusted for alcohol consumption	4	1.03 (1.00, 1.06)	0%	Low	0.43	0.06
Not adjusted for alcohol consumption	5	1.01 (0.95, 1.06)	52%	Moderate		0.38
Adjusted for smoking status	4	1.01 (0.98, 1.05)	31%	Moderate	0.85	0.20
Not adjusted for smoking status	5	1.01 (0.99, 1.03)	0%	Low		0.26
Adjusted for family history of PCa	4	0.99 (0.93, 1.07)	50%	Moderate	0.92	0.05
Not adjusted for family history of PCa	5	1.02 (1.00, 1.05)	17%	Low		0.67
Risk expression
Hazard/rate ratio	2	—	—		—	—
Relative risk	2	—	—		—	—
Odds ratio	5	1.01 (0.99, 1.04)	0%	Low	0.41	0.30

BMI, body mass index; CI, confidence interval; PCa, prostate cancer.

^aThe range of blood DHA concentration in the included studies is 0.55% to 8.73%.

^bDHA, docosahexaenoic acid.