When I see women with polycystic ovary syndrome (PCOS), they are often concerned about what affect coffee will have on their condition. But, do women with PCOS need to avoid coffee?
Some of the claims around coffee in PCOS is that it affects the way glucose is metabolised. This is obviously a concern in PCOS due to the insulin resistance experienced by many.
Another claim around drinking coffee in PCOS is the idea that it can lead to nutritional deficiencies. Some deficiencies are actually linked to reduced fertility. Again, this is a huge area of concern in PCOS.
In this article, I will critique the scientific evidence around drinking coffee in PCOS to provide accurate advice you can trust.
Claim 1: Drinking Coffee in PCOS Increases Blood Glucose Levels
There are currently no studies looking at the affect of coffee in blood sugar levels in women with PCOS.
There is, however, a review that looks at 9 studies on the affect of coffee in diabetes (1). This could be a useful resource as both diabetes and PCOS are conditions which involve insulin not working affectively.
Unfortunately, there are a few problems with this review when looking at it in terms of PCOS. Firstly, only 6 of the studies look at type 2 diabetes which involves the insulin resistance which occurs in PCOS. The other studies look at types of diabetes that are too different to PCOS glucose metabolism to use the results for advice in PCOS.
The next problem is that the studies are all very small, again this reduces their accuracy. And, there are no results looking at the long term effects of the coffee e.g. did this effect weight or fertility?
When we look at the studies in even more detail, the way in which the studies were carried out means that the results become irrelevant for those with PCOS. For example, very high amounts of sugar were used. In one study, a liquid replacement meal of 720 calories and 44g of sugar was eaten for breakfast (2). To have good control in PCOS, a low GI diet is recommended. And, we do not know what these individuals had for lunch and dinner.
Another one of the studies in the review again used very high levels of sugar in the form of 0.5g of glucose / kg (3). So if someone was 12 stone, they would have received 38g of glucose. This time, it was given through a drip. This would affect blood sugars in a completely different way in comparison to eating. This was the only study in the review that looked at insulin levels. Ironically, the results from this particular study showed that insulin levels didn’t change. It is the insulin increase in PCOS which is related to symptoms.
In a further small trial of 10 healthy over weight men with no insulin resistance is also sometimes quoted (4). Again, large carbohydrate loads are given for the trial. Firstly, a meal containing around 75g of carbohydrate is provided the night before the trial and then for the trial a 50g glucose load is given. In addition to this, participants did no exercise 2 days prior to the trial, this is also not recommend in PCOS. The results of this trial were an increase in blood glucose levels with coffee, but again, no increase in insulin levels.
It is also important to remember the reduced accuracy of these studies for use in PCOS, simply of the basis of being in different health conditions.
Claim 2: Does Coffee Cause Magnesium Depletion?
A further claim is that drinking coffee can cause low levels of magnesium. However, the confusion comes from the fact that large amounts of fluid loss in the body can cause magnesium deficiency.
For instance, we often see this in cases with chronic diarrhoea or vomiting. Or in endurance athletes. Hence why the rehydration salts and sports drinks you see contain magnesium.
Caffeine can have a diuretic affect in large amounts, causing you to urinate more, but this is only mild and would not lead to a magnesium deficiency.
In a population based study, it was shown that those who drink more than 6 cups of coffee a day have only a slightly higher eGFR rate than those who drink 1 cup or less (5). eGFR standards for estimated glomerular rate and it is the rate that your kidneys are filtering.
In a small trial, coffee with a content of 6mg / kg showed to have a diuretic affect (6). This would be the equivalent of a 12 stone individual drinking 5 instant coffees in one go. The study also showed that drinking normal coffee at 3mg / kg showed to have no affect.
A larger trial of 72 people showed that coffee did not increase urine output compared with water (7).
Claim 3: Coffee Causes Vitamin B12 Deficiency?
Again, this claim is likely due to the thinking that there is a link with the diuretic affect of coffee.
There is also no evidence that women with PCOS have lower levels of vitamin B12 compared to the general public.
However, where there has been a link is to the use of Metformin in PCOS and a reduced B12 level (8). Metformin is a common medication used to help manage PCOS symptoms.
Vitamin B12 can lead to temporary infertility (9). Fertility is one major area of concern within PCOS and so vitamin B12 for those on Metformin for PCOS does need to be addressed.
Claim 4: Coffee Causes Low Vitamin D Levels in PCOS?
Vitamin D deficiency is higher in those with PCOS than the general public (10). There is as much as a 72.8% vitamin D deficiency prevalence in PCOS compared to 50% in the general UK population (11, 12) . It is thought that this deficiency may be linked to some of the PCOS symptoms.
The only study looking at coffee and vitamin D levels has been done in healthy teenagers (13). The results suggest a link between increased coffee intake and increased levels of vitamin D. However, the study does not control all factors and so it is not 100% proof that this is the case. Also, a healthy teenager’s body works extremely differently to those with PCOS.
Unfortunately, there appears to be no proven benefit for PCOS symptoms when using vitamin D supplements. This result was shown in a meta-analysis looking at 9 studies (14).
Please note, that whilst there may be no benefit to PCOS symptoms directly, vitamin D supplements are recommended for other health reasons for the general public. Please click here to find out more.
So What Do I Advise?
As there is no evidence to support the idea that those with PCOS should avoid coffee or caffeine. I advise my clients to follow the general healthy guidelines of 400mg of caffeine/ day (15).
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