Canadian researchers reviewed previous studies and identified some potential risk factors for primary brain tumors in children and adults.

For adults, genetic variants, pesticide exposure, occupation farming/hairdressing, consumption of processed meat and personal use of hair dye are linked to elevated risk for primary brain tumors. 

The potential risk factors for brain tumors in children include high birth weight, childhood exposure of pesticides, parental occupational exposure to pesticides, and maternal consumption of processed meat during pregnancy.  

Some evidence suggests that material intake of prenatal supplements may decrease risk of brain tumors in children.  Individuals with certain genetic variants and a history of allergy may be at lower risk for brain tumors.

Some long-term studies suggest that exposure to electromagnetic radiofrequencies or radiation emitted from wireless devices like smart phones may increase risk for malignant brain tumors, but the review does not include studies of that type.

The majority of risk factors for brain tumors can be modified to lower the risk.  Other measures may also be taken to lower risk of brain tumors such as taking vitamin C supplements.

A study report released in 2015 in Neuroepidemiology suggests that taking vitamin C supplements may lower risk of glioma, a type of malignant brain tumor. 

The review went through 15 studies and found that vitamin C intake was associated with reduced risk of glioma.  The risk reduction was up to 20%.  (David Liu)

Sources:

1) Zhou S, Wang X, Tan Y, Qiu L, Fang H, Li W.  Association between vitamin C intake and glioma risk: evidence from a meta-analysis. Neuroepidemiology. 2015;44(1):39-44. Epub 2015 Feb 17.

2) Quach P, Sherif RE, Gomes J, Krewksi D.  A systematic review of the risk factors associated with the onset and progression of primary brain tumours.  Neurotoxicology. 2016 May 17. pii: S0161-813X(16)30087-0. doi:  10.1016/j.neuro.2016.05.009.