True or False: Mycotoxins in Coffee Are a Serious Threat to Our Health and the Only Way to Avoid Them is Abstinence

As we are about to see coffee is by far not the worst aflotoxin offender in the human diet. Still, that does not mean that the coffee related exposure to this form of mold that can befall all sorts of grains, nuts and seeds is harmless.

You will probably remember that I casually touched on the possibility of being exposed to aflotoxins and more importantly ochratoxins as a result of the consumption of mold-infected coffee in previous coffee articles. When the issue of the « coffee ➲ aflotoxin / ochratoxin exposure ➲ serious health » triage resurfaced in a brief facebook conversation, recently, I realized that I was not 100% sure if these mycotoxins that are produced by Aspergillus flavus, Aspergillus ochraceus, Aspergillus niger, and Aspergillus carbonarius do or don't pose a serious health risk.

Well, you know how much I hate unanswered questions, so I kept digging until I'd found what I consider to be a half-way satisfying answer to this life-or-death question ;-)
"The amount of aflotoxin in the average cup of coffee is a serious threat to our health!"

In 90% of the cases the above statement is FALSE! Despite the fact that it is difficult to tell how much mycotoxins you've been flushing down with your morning coffee today, the exact amount of the more common aflotoxins and their similarly kidney-toxic, pro-carcinogenic and coffee-loving cousins, the ochratoxin, in the average cup of (roasted) coffee is probably way too low to be worried about.

Figure 1: Mycotoxin exposure from coffee; calculated based on data from Europe (Vd Stegen. 1997)

Based on the studies I have reviewed for this article, it appears almost certain to say that the relatively low amount of coffee beans per cup (4-8g) reduces your average mycotoxin exposure from 1-4 cups of coffee per day to levels that are almost certainly within one of the various (multi-)national reference ranges (Van Egmond. 2007):
Using a selection of commercially available regular and soluble coffee brands, van der Stegen et al. have actually calculated the average daily mycotoxin intake of Europeans with an average coffee consumption of 1-4  to be in the nanogram range - 19ng and 10ng, specifically, for regular and instant coffee drinkers, respectively.
Just to make sure, we understand each other, here: That's 1000x less than you'd get from only 20g of some of the Brazilian peanuts Freitas and Brigido analyzed in a 1998 study for their mean and maximal mycotoxin content. With 1099µg/kg the worst offenders in this study would easily have you breach the already lax American (North & Latin America) max. tolerable intake limit of 20µg/kg per day - and that despite the fact that this limit is more than 1000x higher than the amount of mycotoxins you'll have in your average cup of coffee.

Green vs. roasted coffee: Do we have to chose between anti-oxidants and mycotoxins?

It goes without saying that the mere fact that the dangers of being exposed to high amounts of mycotoxins from adequately processed and stored coffee appears negligible, does not warrant ignoring the problem completely. The effects of processing and storage are and will thus always be an important issue.

Given the fact that humid and cool (but not cold) is what mold needs to thrive, you will probably already have suspected that the hot and arid environment of a coffee roastery is not exactly the favorite growth environment for the Aspergillus family.

Figure 2: Ochratoxin content (µg/kg) in green, roasted & soluble coffee, left; total antioxidant activity in TROLOX essay of green (=unroasted), lightly, medium and dark roast coffee (Blanc. 1998; del Castillo. 2002)

A lower mycotoxin content is yet not the only beneficial effect of roasting. Contrary to what 99% of the people will tell you, when you ask them, the roasting process increasesnotdecreases the total antioxidant capacity of coffee (TAC).

Due to the formation of a whole host of new antioxidant molecules during the roasting process, light or mildly roasted coffee beans have a higher total antioxidant capacity than green ones - irrespective of the reduced chlorogenic acid content, for which the green beans are currently (over-)hyped. If you look at the data in Figure 2 you will see that even the heavily roasted, tar-black coffee beans still have a minimally higher anti-oxidant activity than the "natural" green coffee beans (del Castillo. 2002) - an observation that has been made both in the Petri dish, as well as ex vivo rodent studies (Daglia. 2002).

You've been drinking tons green coffee, lately?

Don't worry! Your past green coffee consumption probably isn't a real problem either. It does after all look as if those beans were yet another example for the infamous "nature kows best" principle. I mean, can it really be "coincidence" that the beans come with "anti-mycotoxin agents" in form of cafestol and kahweol. These coffee-specific diterpenes have been shown to ameliorate the aflotoxin B induced genotoxicity (Cavin. 1998) and the subsequent pro-carcinogenic effects (Cavin. 2001) and can be expected to exert protective effects against ochratoxin toxicity, as well.

In view of the fact that similar evidence exists for chlorogenic acids (CGA), dodecyl chlorogenates (DCGA) and a high(er) coffee consumption, in general (Suárez‐Quiroz. 2013; Ferk. 2013), it is actually not surprising that studies like Shank et al. (1972)  or Bulatoa-Jaym et al. (1982) found links between aflotoxin contaminated corn, grains, potato, peanuts & co., but could not identify an increased risk in liver cancer for coffee aficionados. Consequently, it's (imho) relatively unlikely that your health has already taken a beating - irrespective of the amount of the number of cups of green coffee you've been consuming over the past weeks.
I would still like to remind you that even the sum of the previous remarks must not be misunderstood as an incentive to willy nilly forget all previously harbored concerns about "moldy coffee beans"... and I say this in spite of the existing epidemiological evidence that a high coffee consumption decreases the risk of developing and dying from liver cancer (Kurozawa. 2005; El–Serag. 2007). The liver is after all not the only organ that may be affected by the pro-carcinogenic toxins. The kidneys are at least as susceptible to the toxic assault from the mycotoxin filtrate that passes through them.

The liver is not the only organ that's taking a beating

It may thus be hypothetical, but not impossible that a 2x / 2.6x increased risk to develop renal cell carcinoma Mimi et al. report in a 1986 paper on the associations between coffee consumption and kidney cancer may at least be partially related to the higher mycotoxin exposure in those 61 study participants who consumed 1-4 cups of coffee per day (Mimi. 1986).

That mycotoxins can promote the development of kindey cancer had been demonstrated 17 years before the publication of Mimi's paper by Epstein, Bartus & Farber (1969) whose Wistar rats developed renal epithelial neoplasms after being exposed to food-borne aflatoxin B1.

Table 1: Incidence of renal epithelial and malignant hepatic tumors in male Wistar rats ingesting aflatoxin B1 for 147 days; the indces a, b, c provide irrelevant (in this context) extra information (Epstein. 1969)

In that, it's quite remarkable that even the lowest aflotoxin dosage the researchers used in their study (0.25µg/kg chow; HED  ~1.2ng/kg body weight, ; see Table 1) lead to significant rates of cancerous growth in both kidney (28%, if we count both developing and full-blown renal neoplasms) and liver  within the 21 week study period.

There is just one no-go: Storing unroasted beans for years in your humid basement

In view of the large regional difference in aflotoxin infection rates, the different susceptibility of the various coffee cultivars and the influences of weather, storage conditions, blending, processing, and all the other factors that increase or decrease the amount of mold and mycotoxins on coffee (see Figure 3), I would still be hesitant to exclude the possibility that stocking up on highly aflotoxin contaminated unroasted coffee you possibly even stock in a very humid basement of yours to consume the coffee over the course of months if not years could have negative effects on the health of your organs, in general, and the function of your kidney and liver, in particular.

Figure 3: Percent infection of coffee cherries and beans byAspergillusspecies potentially capable of producing ochratoxin A in four Brazilian coffee growing regions from the 1999 and 2000 harvests (Taniwaki. 2003)

I mean, look at the data in Figure 3. It's probably no coincidence that the otherwise virtually uninfected beans of coffee from the 1999 and 2000 harvests in the Cerrado Miniero exhibits a 4% infection rate after being stored intermediately before it is either roasted, shredded or both or simply forwarded "raw" to the mailbox of an "unroasted coffee enthusiast". Similar effects can be expected when the huge coffee manufacturers mix harvests from various regions. If only one is infected, all it takes to have Aspergillus flavus literally "all over the place" is enough time in one of the huge storage silos or the hold of one of the container ships that transport coffee from the "New" back into the "Old World".
References:

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• Blanc, M., Pittet, A., Muñoz-Box, R., & Viani, R. (1998). Behavior of ochratoxin A during green coffee roasting and soluble coffee manufacture. Journal of agricultural and food chemistry, 46(2), 673-675.
• Bøhn et al. (2013) Coffee and cancer risk, epidemiological evidence, and molecular mechanisms. Molecular Nutrition & Food Research [early view article]
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