A new study suggests that the supplements may play a critical role in reducing the devastating impact of air pollution.
In a trial on humans, scientists found just small doses could offset the deadly damage caused by tiny, toxic particles.
Experts believe the findings could have a significant public health benefit in heavily polluted cities across the world.
The World Health Organization estimates that 92 per cent of the world's population currently live in areas where pollution exceeds safety guidelines.
Considered the most dangerous form, PM2.5 includes various toxins like sulfate and black carbon.
These can penetrate deep into the lungs or cardiovascular system as a result of breathing them in.
Previous research has shown there to be no 'safe' level for humans, and long-term exposure is known to reduce life expectancy.
It is believed that they cause health damaging epigenetic changes - mechanisms that can switch genes on and off.
And the new study, published in PNAS, shows that the tiny particles can switch off cells in the immune system, the BBC reports.
The researchers, from Columbia and Harvard universities, used volunteers who were aged between 18 and 60 who were deemed medically healthy.
They were either given a placebo, or a supplement containing 2.5mg of folic acid, 50mg of B6 and 1mg of vitamin B12.
Wearing a facemask, the patients were exposed to particles from a heavily trafficked street in Toronto. Blood samples were also taken.
Study author Dr Jia Zhong, from Harvard University, said: 'The health effects of air pollution and how it plays a role in one's health raise many complex issues.
'Until we can attack the problem on an individual level we are a long way from fully tackling its challenges for the public's health.'
However, the scientists were keen to point out that further research is needed to validate the findings, especially in heavily polluted cities.
Professor Andrea Baccarelli, of Columbia University, said: 'While emission control and regulation is the backbone of prevention, high exposures are, unfortunately, the rule still in many megacities throughout the world.
'As individuals, we have limited options to protect ourselves against air pollution.'
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