Following the last post which concluded that for the majority of the population, the radicals produced during exercise were beneficial, and shouldn’t be neutralised artificially, I was asked about how this relates to taking vitamin C post workout to reduce the cortisol levels released from exercising. Many body-builders and athletes will take 1g of vitamin C post workout, with the interest of inhibiting cortisol production, because cortisol inhibits testosterone and protein synthesis. So here,I’ll discuss cortisol level changes during and after exercise, what this means to your recovery, and the effects of taking vitamin C post exercise.


Cortisol production from exercise

The function of cortisol is essentially to get the body prepared to for the stress of exercising. Some of the ways it does this is by stimulating the release of glucose/ fatty acids for energy, and inhibitng functions which are not needed for exercise such as protein synthesis.

Not all exercise will result in a cortisol spike, and any exercise which operates at 40% of your VO2max will actually slightly lower your cortisol levels1. However, any exercise which goes about 60% of your VO2max will cause a significant spike in cortisol levels, and this encompasses any exercise which you would class as strenuous. The amount of cortisol released by exercising is directly related to the intensity of exercise, i.e the harder you push yourself, the more cortisol will be released.

Below you can see a graph of cortisol production before, during (at the 15min mark) and after exercising at 85% VO2max2 for 15 mins. You can see that exercising causes a very sharp spike in cortisol levels during exercising, which can be 50% above resting cortisol levels, but quickly drops down below resting cortisol levels within about half an hour, and eventually normalises after about an hour and a half.


graph 1

Interestingly, the reduction in cortisol doesn’t seem to be a result of stopping exercising. This second graph (below) shows cortisol levels of individuals during prolonged ‘relatively intense exercise’ (think doing a cross-country run). Cortisol levels take a spike, but even though exercise continues cortisol levels decrease within less than an hour3. (The difference in values and time scales between the graphs is a result of the different methods used to measure cortisol). I can speculate that a reason for this is that the effects of cortisol (such as release of free fatty acids) is no longer needed, as hormones such as epinepherine (adrenaline) stimulate the release of FFAs, and levels of epinepherine continue to raise throughout exercising.

This would suggest that taking vitamin C post workout would have very little benefit on cortisol levels anyway, because they are already decreasing. The only way in which vitamin C has been shown to inhibit exercised induced cortisol effectively is taking it pre-workout, and we have already discussed the negative implications of doing this.


graph 2

Vitamin C and cortisol

Vitamin C does inhibit cortisol released by adrenaline stimulation, possibly by as much as 30%, and this relationship is well documented4,5,6. Interestingly, vitamin C supplementation seems to have no effect on resting cortisol levels, so if you cortisol levels are already high, perhaps from stressful job or taking a load of caffeine before you workout, you will need to look at other ways to reduce your cortisol.


Cortisol’s relationship with testosterone

At resting, cortisol levels have no impact on testosterone levels, and it is only when cortisol reaches a certain threshold that it start to impact testosterone. As exercising spikes cortisol levels it is possible that it can have a negative impact on testosterone levels, which is something most athletes want to avoid. As vitamin C’s ability to suppress cortisol production is well documented many athletes will take some vitamin C (usually 1g) post workout.

Research has shown that although cortisol reduces total testosterone (TT) after exercise, the amount of free testosterone (fT) actually increases7. From the table, you can see that after exercising, total testosterone is reduced by about 11.5%, whereas free testosterone has increased by 38.4%. These findings supported by other studies which have found that after exercise free testosterone has increased by similar amounts8.


* denotes significant (p ≤ 0.01) difference from the respective resting value.

Free testosterone is also sometimes referred to as bioavailable testosterone, and it is free testosterone which is an indicator for anabolic potential. Total testosterone includes free testosterone, but also include testosterone which is bound to proteins such as albumin, which prevents them from binding to muscle cells. So, although exercising looks to reduce total testosterone, it actually increase the amount of free testosterone – which is good.

Why does this happen? – It is possible that because cortisol and testosterone have the same precursor molecules (see diagram 1), more testosterone is  produced almost by accident, just because more precursors are made (Ok, so nothing in biology is by accident, rather by cleaver evolutionary design). Another reason for there being more free testosterone is that cortiol and testosterone both compete for the same binding sites on proteins such as albumin, and as more cortisol is produced it causes testosterone to disassociate from these binding sites. Finally, we know that changes in pH and temperature cause protein binding affinity to change – this is how the body delivers more oxygen to working muscles. So it is very possible that changes in pH or temperature can reduce the binding affinity of albumin (and other proteins) to testosterone – producing more free testosterone.


diagram 1


It looks like we have a similar conclusion to the previous article – the body knows best when it comes to exercising, so don’t try and out smart it. Although on the surface it may seem like taking vitamin C to reduce production of the dreaded cortisol monster is a clever thing to do, it probably isn’t. The bodies natural response to exercise is well suited for its recovery, and this includes the production of cortisol, which actually produces more free testosterone which will help with the growth/ recovery process. Besides, from looking at graph 1, which shows serum cortisol shoots up during exercising, and drops relatively quickly, you can see that if you wanted to inhibit cortisol production you would need to be taking vitamin C before your workout, which we have already ascertained can inhibit the stimulation of important growth/ repair signals.

I would be more worried about prolonged cortisol exposure from your lifestyle rather than the acute exposure you would get from exercise (hell, I’d even embrace the acute exposure). I’d say your exercising would benefit more from taking measures to reduce stress than taking vitamin C post exercise.




1. Hill EE. (2008). Exercise and circulating cortisol levels: the intensity threshold effect.. J Endocrinol Invest. 31 (7), 587-91.

2. Michael A Starks. (2008). The effects of phosphatidylserine on endocrine response to moderate intensity exercise. JISSN. 5 (11), 550-2783.

3. Physiology of sport and exercise”, fourth edition; Jack H. Wilmore, David L. Costill, W. Larry Kenney.

4. Liakakos D. (1975). Inhibitory effect of ascorbic acid (vitamin C) on cortisol secretion following adrenal stimulation in children.. Clin Chim Acta. 65 (3), 251-5.

5. Peters EM. (2001). Attenuation of increase in circulating cortisol and enhancement of the acute phase protein response in vitamin C-supplemented ultramarathoners.. Int J Sports Med. 22 (2), 120-6.

6. Peters EM. (2001). Vitamin C supplementation attenuates the increases in circulating cortisol, adrenaline and anti-inflammatory polypeptides following ultramarathon running.. Int J Sports Med. 22 (7), 537-43.

7. Kaye K. Brownlee. (2005). Relationship Between Circulating Cortisol and Testosterone: Influence of Physical Exercise. J Sports Sci Med. 4 (1), 76-83.

8. Zmuda JM. (2996). Exercise increases serum testosterone and sex hormone-binding globulin levels in older men.. Metabolism. 45 (8), 935-9.

Image courtesy of runare.

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