The government may overlook periods, but we certainly don’t.

Part I of this series covered an overview of creatine and its mechanism of effect. We also touched on the main differences between males and females, and how that may affect creatine utilisation and efficacy in the body. This sets us up lovely to discuss the impact of the menstrual cycle on creatine metabolism.

Let’s Just Circle Back

So, you already know this from your reading of Part I, but buckle up because this one is a shocker: females have different characteristics to men. Overall, females differ from men in the fact that they:

• Bleed from their internal organs once a month for 20+ years.
• Produce less creatine
• May have a lesser storage capacity for creatine as they have lower muscle mass
• Have a lower rate of creatine excretion

And, to briefly summarise the main role of creatine in the body:

• Creatine is used to generate ATP (energy) via the phosphocreatine cycle
• Creatine kinase is the enzyme that influences this
• Creatine kinase is also used as an indirect biomarker of muscle damage (although research is a bit iffy on how accurate it reflects exercise-induced muscle damage).

Owing to the chaos that is being a female that has the capacity to reproduce, the resulting hormonal shitshow alters creatine synthesis, transport, creatine kinase concentration/metabolism and creatine bioavailability[1]. This offers huge considerations and may actually be a huge draw for females to incorporate a creatine supplement into the diet.

Chapter 1: My First Period

The menstrual cycle is hypothesised to influence creatine levels in the body, owing to the changes in female sex hormones during the cycle. Unfortunately, most of the research is currently majority animal-based, and a lot less clear-cut. However, the current theoretical model of creatine-kinase and menstrual cycle hormone interaction is really well-illustrated below:

Smith-Ryan et al. (2021)

You can clearly see that CK levels are lowest in the follicular phase, or the pre-menstrual stage. Creatine kinase levels peak around menstruation and ovulation, and remain high in the early stage of the luteal phase, before decreasing as the luteal phase comes to an end. Creatine kinase levels typically mirror that of oestrogen, as indicated by some rodent studies[2]. It is hypothesised that this high level of oestrogen evident in the luteal phase can help “spare” creatine kinase and lead to less muscle damage, but this is currently only investigated in the context aerobic exercise[3].

Metabolic Impact of Menstruation

You can see from the diagram further up that oestrogen levels are highest during the luteal phase (end of the menstrual cycle). Oestrogen aids in the promotion of lipid oxidation, and encourages the sparing of glycogen[4]. The opposite is true for progesterone, and this is evident in the reduced capacity for carbohydrate storage during the follicular phase.

Intramuscular creatine may also enhance glycogen levels (and therefore increase exercise performance!). Intra-muscular creatine may also influence carbohydrate and protein metabolism[5].

Therefore, it may be beneficial for females to supplement with creatine, particularly in the follicular phase to help offset this natural reduction in glycogen storage capacity.

Conclusions

Whilst we must employ the age-old adage of further research is needed before we hang our hat on any solid conclusions from the current knowledge-base, it does provide some interesting considerations and questions:

• Can creatine supplementation help offset muscular damage?
• Can creatine offset the reduction in glycogen storage in the follicular phase of the menstrual cycle?
• If so, should we be encouraging females to supplement at certain stages in the menstrual cycle?

We don’t currently know for sure, but basically the current thinking is it can’t hurt[6].

And finally, with our background firmly established, and female-specific considerations for creatine considered, we can FINALLY get into the meaty part of the science in Part III – the benefits of creatine supplementation for women.

Reference List

1. Smith-Ryan, A.E., Cabre, H.E., Eckerson, J.M., Candow, D.G. (2021) ‘Creatine Supplementation in Women’s Health: A Lifespan Perspective’, Nutrients, 13(3), pp. 877.
2. Somjen, D., Weisman, Y., Harell, A., Berger, E., Kaye, A.M. (1989) ‘Direct and sex-specific stimulation by sex steroids of creatine kinase activity and DNA in synthesis in rat bone’, Proceedings of the National Academy of Sciences, 86, pp. 3361-3365.
3. Williams, T., Walz, E., Lane, A.R., Pebole, M., Hackney, A.C. (2015) ‘The effect of estrogen on muscle damage biomarkers following prolonged aerobic exercise in eumenorrheic women’, Biology of Sport, 32(3), pp. 193-198.
4. Isaaco, L., Duché, P., Boisseau, N. (2012) ‘Influence of hormonal status on substrate utilization at rest and during exercise in the female population’, Sports Medicine, 42(4), pp. 327-342.
5. Volek, J.S., Rawson, E.S. (2004) ‘Scientific basis and practical aspects of creatine supplementation for athletes’, Nutrition, 20(7-8), pp. 609-614.
6. Antonio, J., Candow, D.G., Forbes, S.C., Gualano, B., Jagim, A.R., Kreider, R.B., Rawson, E.S., Smith-Ryan, A.E., Van Dusseldorp, T.A., Willoughby, D.S, Ziegenfuss, T.N. (2021) ‘Common questions and misconceptions about creatine supplementation: what does the scientific evidence really show?’, Journal of the International Society of Sports Nutrition, 18(1), pp. 1-17.