Can High-Dosage Biotin Increase Cancer Risk?

Micronutrients like biotin are crucial to DNA metabolism and repair, helping to maintain DNA stability. This is important because unstable and/or damaged DNA, characterized by chromosome damage or malsegregation, has been identified as a beginning step in the potential development of cancer. Despite these known DNA-stabilizing effects of biotin, results of a study published in 2005 seem to conversely suggest that high levels of dietary biotin intake may be linked to DNA damage.^{7, 63}

One way to measure DNA damage is to assess the formation of micronuclei (MN) in dividing cells, which form from fragmented or lagging chromosomes that have not properly segregated and reattached in daughter cells as the parent cell divides. The formation of MN is associated with the DNA instability seen in cancer development.^{63, 74}

In a 6-month study involving 196 volunteers (excluding any with known major diseases or pregnancy), researchers assessed the formation of MN after six months of antioxidant supplementation. Participants underwent a baseline blood test and completed a food frequency questionnaire at the beginning of the study, and were required to discontinue any other vitamin supplementation. They were then randomly assigned to take the antioxidant mix or to the control group.⁶³

Both groups had a second blood test at study end, and a small subset of participants (22 test and 22 control group subjects) agreed to a blood test three months into the study to assess plasma antioxidant changes and MN formation. Biotin and other micronutrient intakes were calculated, however, solely by questionnaire responses.⁶³

Each micronutrient's effect on MN formation was extrapolated from comparison of intake to the blood test results showing the level of MN formation at the beginning of the study. Using these study protocols and method of analysis, the highest third tier of dietary biotin intake (as calculated from the questionnaires) corresponded to a 65% higher level of MN frequency than the lowest biotin intake group. There was no corresponding increase in MN frequency at the lowest and mid-level biotin-intake groups.⁶³

The study researchers suggest that these results combined with other tests may indicate that 600 μg /day of biotin could be the tolerable upper intake level without deleterious effects. They note that eggs, a rich source of the three micronutrients that higher intakes of correlated with increased MN frequency, have been linked to increased risk of colon and pancreatic cancer in population studies also conducted by food frequency questionnaires.⁶³

However, it should be noted that while a medium egg contains 11 µg of biotin, lentils and soy have similar to significantly more biotin per serving size: 13.0 µg and 17.5 µg respectively. Both of these foods, higher in biotin then eggs, have been linked to lower cancer risks. Additionally, biotin is essential for biotinylation of histone, a DNA-binding molecule crucial to chromosome structure and DNA stability - which minimizes risk of cancer in human cells.^{7, 11}