I have used frequent B12 shots as an analgesic for resistant pain cases. For men over 40, 10 yr. use of injectable B12 is linked to doubling lung cancer risk.
Brasky, Theodore M., Emily White, and Chi-Ling Chen.
Long-term, supplemental, one-carbon metabolism–related vitamin b use in relation to lung cancer risk in the Vitamins and Lifestyle (VITAL) cohort.
Journal of Clinical Oncology 35.30 (2017): 3440-3448.
http://ascopubs.org/doi/abs/10.1200/JCO.2017.72.7735?journalCode=jco
- took subjects over 50 so people under 40 not researched
- 77,118 participants
- looked at 10 years exposure
- risk of lung cancer was doubled in men, though not women, if injectable or single use used.
- Those who smoked as well could get up to four times risk
- No effect for those on multivitamins only
Comment – have to apologize for males taking frequent B12 shots for pain. Certainly, for those 40 and over, not an option for smoking men.
Lifelong risk of lung cancer for a nonsmoking male is 13/1000 – or 1/76
Can J Public Health. 1994 Nov-Dec;85(6):385-8.
Lifetime probability of developing lung cancer, by smoking status, Canada.
Villeneuve PJ et al
https://www.ncbi.nlm.nih.gov/pubmed/7895211
“It was found that 172/1,000 of male current smokers will eventually develop lung cancer; the similar probability among female current smokers was 116/1,000. For those who never smoked on a regular basis the lifetime risk was substantially reduced. Only 13/1,000 males and 14/1,000 females in this category will develop lung cancer. When smoking status is not adjusted for, the lifetime risk of developing lung cancer is approximately 96/1,000 and 43/1,000 for males and females respectively.”
Comment – non vitamin male users in total had a 175/14120 = 13/1000 risk of lung cancer
Vitamin B12 use in males had a 69/4885 = 14/1000 risk of lung cancer.
given usual risk is 13/1000 I doubt the 1/1000 extra risk is significant.