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The B-complex vitamins are popular to take for energy, improved cognitive function, or to counter a deficiency. To evaluate whether vitamin B supplementation is actually needed, we reviewed the literature for impacts on cognitive function and energy. We combined this review with deficiency rates and our knowledge of deficiency symptoms. In general, we reserve B-complex supplementation for those that can't get enough in their diet, such as vegans who can't access B12 in animal-based foods.
For background, the B vitamins are essential vitamins required for proper metabolic function. Without B1 and B3, the body cannot produce the energy it needs. Without B6, hundreds of metabolic reactions are hampered, especially those related to protein metabolism. Without B12, the central nervous system, red blood cells, and DNA synthesis cannot function properly. Deficiencies in these vitamins lead to weight loss, neurologic breakdown, weakened immunity, skin irritation, and full-blown deficiency diseases like beriberi and pellagra.
Clearly full-blown deficiencies are bad, but most people get enough of these vitamins in their diets, as shown below (note that full-blown deficiencies are rarer). Usually, deficiencies in America are not caused by suboptimal intake, but rather caused by an inability to absorb these vitamins. Vitamin B12 is an exception, since it is only available in animal-based products, which vegetarians and vegans often don't get enough of.
So what does the evidence say about supplementation?
In conclusion, the evidence for B-complex supplementation benefits is insufficient to support claims for cognitive function, energy, mood, mortality, cancer, or cardiovascular benefits. However, if a deficiency or dietary restriction is suspected, then B-complex supplementation makes sense to avoid symptoms of full-blown deficiencies.
A systematic review of the literature found only one older study on the energy impacts of b complex supplementation, which focused on blood serum indicators of energy and was not enough to draw conclusions off of (2).
Source: Markun, 2021 (2).
In a systematic review of 16 trials evaluating cognitive impacts of B complex and vitamin B12 in individuals without neurologic issues, no statistically significant impact on cognitive function was found (1). Another systematic review focused on older individuals with dementia symptoms and low B12 levels. This review found 3 trials that met the criteria, but B12 supplementation did not have a statistically significant impact on cognitive function. Overall, there is insufficient evidence to suggest that B complex or B12 provides cognitive benefits, except when serious deficiency levels are reached.
Source: Markun, 2021 (1). Malouf, 2003 (2).
One systematic review found that b-complex improved mood in a majority of studies included, but this study was funded by the nutritional supplements industry and did not have good selection criteria. In fact, they most of the studies included had interventions that also included vitamin D and other supplements along with the b-complex vitamins. (5). As a result of the bias, evidence is insufficient to say whether mood is improved.
Source: Young, 2019 (5).
No studies met the quality requirements for determining the impact of vitamin b6 impact on cancer.
Source: US Preventive Services Task Force, 2018 (4).
No studies met the quality requirements for determining the impact of vitamin b6 impact on cardiovascular disease.
Source: US Preventive Services Task Force, 2018 (4).
Insufficient evidence was available for determining the impact of vitamin B3 or vitamin B6 on mortality.
Source: US Preventive Services Task Force, 2018 (4).
