Comparison 1. B vitamins versus control.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Overall cognitive functioning	10		Std. Mean Difference (Random, 95% CI)	Subtotals only
1.1 3‐12 months of supplementation (final measurement data)	3	2556	Std. Mean Difference (Random, 95% CI)	0.00 [‐0.08, 0.08]
1.2 3‐12 months of supplementation (change from baseline data)	2	317	Std. Mean Difference (Random, 95% CI)	‐0.03 [‐0.26, 0.19]
1.3 > 1‐2 years of supplementation (final measurement data)	5	6956	Std. Mean Difference (Random, 95% CI)	‐0.01 [‐0.08, 0.06]
1.4 > 1‐2 years of supplementation (change from baseline data)	1	241	Std. Mean Difference (Random, 95% CI)	0.06 [‐0.20, 0.31]
1.5 > 2‐5 years of supplementation (final measurement data)	4	3985	Std. Mean Difference (Random, 95% CI)	‐0.01 [‐0.11, 0.09]
1.6 > 5‐10 years of supplementation (final measurement data)	3	10249	Std. Mean Difference (Random, 95% CI)	‐0.01 [‐0.09, 0.07]
2 Episodic memory	10		Std. Mean Difference (Random, 95% CI)	Subtotals only
2.1 3‐12 months of supplementation (final measurement data)	4	1442	Std. Mean Difference (Random, 95% CI)	0.02 [‐0.08, 0.12]
2.2 3‐12 months of supplementation (change from baseline data)	2	430	Std. Mean Difference (Random, 95% CI)	0.04 [‐0.15, 0.23]
2.3 > 1‐2 years of supplementation (final measurement data)	4	5625	Std. Mean Difference (Random, 95% CI)	0.05 [‐0.03, 0.13]
2.4 > 1‐2 years of supplementation (change from baseline data)	1	241	Std. Mean Difference (Random, 95% CI)	0.06 [‐0.19, 0.32]
2.5 > 2‐5 years of supplementation (final measurement data)	3	3523	Std. Mean Difference (Random, 95% CI)	‐0.05 [‐0.15, 0.05]
2.6 > 5‐10 years of supplementation (final measurement data)	1	1053	Std. Mean Difference (Random, 95% CI)	‐0.10 [‐0.22, 0.02]
3 Executive function	7		Std. Mean Difference (Random, 95% CI)	Subtotals only
3.1 3‐12 months of supplementation (final measurement data)	3	536	Std. Mean Difference (Random, 95% CI)	0.14 [‐0.18, 0.46]
3.2 3‐12 months of supplementation (change from baseline data)	1	171	Std. Mean Difference (Random, 95% CI)	0.39 [0.07, 0.71]
3.3 > 1‐2 years of supplementation (final measurement data)	3	2976	Std. Mean Difference (Random, 95% CI)	‐0.01 [‐0.15, 0.13]
3.4 > 2‐5 years of supplementation (final measurement data)	2	2648	Std. Mean Difference (Random, 95% CI)	‐0.06 [‐0.13, 0.02]
3.5 > 5‐10 years of supplementation (final measurement data)	1	1049	Std. Mean Difference (Random, 95% CI)	0.02 [‐0.10, 0.15]
4 Speed of processing	7		Std. Mean Difference (Random, 95% CI)	Subtotals only
4.1 3‐12 months of supplementation (final measurement data)	2	289	Std. Mean Difference (Random, 95% CI)	‐0.04 [‐0.28, 0.19]
4.2 3‐12 months of supplementation (change from baseline data)	3	487	Std. Mean Difference (Random, 95% CI)	0.12 [‐0.34, 0.58]
4.3 > 1‐2 years of supplementation (final measurement data)	2	1030	Std. Mean Difference (Random, 95% CI)	0.03 [‐0.09, 0.15]
4.4 > 1‐2 years of supplementation (change from baseline data)	1	241	Std. Mean Difference (Random, 95% CI)	‐0.04 [‐0.29, 0.21]
4.5 > 2‐5 years of supplementation (final measurement data)	1	818	Std. Mean Difference (Random, 95% CI)	‐0.08 [‐0.22, 0.06]
5 Incidence of MCI or dementia	1		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
5.1 > 2‐5 years of supplementation	1	1803	Risk Ratio (M‐H, Random, 95% CI)	1.01 [0.69, 1.48]
6 All‐cause mortality	4		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
6.1 3‐12 months of supplementation	1	201	Risk Ratio (M‐H, Random, 95% CI)	0.34 [0.01, 8.33]
6.2 >1 to 2 years of supplementation	1	3680	Risk Ratio (M‐H, Random, 95% CI)	0.86 [0.66, 1.11]
6.3 >2‐5 years of supplementation	1	1127	Risk Ratio (M‐H, Random, 95% CI)	1.98 [1.22, 3.21]
6.4 >5‐10 years of supplementation	1	12064	Risk Ratio (M‐H, Random, 95% CI)	1.03 [0.95, 1.12]