“If our findings are confirmed by larger studies, women who receive oral contraceptives may be considered for coenzyme Q10 and/or alpha-tocpherol supplementation,” wrote lead author Prabhudas Palan from the Albert Einstein College of Medicine in New York.

Coenzyme Q10 and alpha-tocopherol (a form of vitamin E) are both lipid-soluble antioxidants found in cell membranes. They are capable of reducing the amount of free radicals that can lead to oxidative stress which has been linked to a variety of significant diseases such as   Alzheimer's, cardiovascular disease and cancer.

The researchers recruited 55 pre-menopausal women (average age 33) with regular menstrual cycles. 15 women were taking an oral contraceptive (OC) (norgestimate/ethinylestradiol) while the other 40 were not taking any (OC). Women already taking multivitamins or Co-Q10 supplements were excluded.

Non-fasting blood samples were taken randomly during the menstrual cycle allowing serum levels of a variety of antioxidants to be accurately measured. These showed gamma-tocopherol, alpha- and beta-carotene, and lycopene levels were similar between the groups. However, serum levels of Co-Q10 were 37 per cent lower in the OC group, and alpha-tocopherol levels were 24 per cent lower.

“The results clearly show that the use of OC significantly lowered the serum levels of coenzyme Q10 and alpha-tocopherol, compared with levels in non-OC users,” wrote the researchers, who concluded “The potential value, if any, for coenzyme Q10 and alpha-tocopherol supplementation in OC users and the effect of menstrual cycle phase on oxidative stress deserve further investigation.”