I was recently interviewed by the ABC for a story on the safety of caffeine strips*. The story was aired today (for the video and transcript see here), with my section coming at the end. In a short TV piece it is difficult to convey the subtleties of the issues involved, so please indulge me as I use this forum to enlarge on my brief comments.
What are caffeine strips?
Caffeine strips are a method of packaging caffeine into what looks like an ordinary stick of chewing gum, but thinner. They rapidly dissolve in the mouth, which the manufacturers claim makes absorption of caffeine faster. I’ll deal with this claim later.
While caffeine strips have been on the US market for a while, this is the first time I am aware of that caffeine strips have been sold in Australia. The brand being marketed now comes as a pack of 5 individually wrapped strips, each strip containing 40 milligrammes (mg) of caffeine. The packet has a warning “contains caffeine” on the front, and a warning on the back not to consume more than 5 strips in a day (and that the strips are not suitable for children and pregnant women).
This is clearly being targeted primarily at the sports market (although study and work gets a nod as well), with the emphasis on rapid absorption and low bulk. For high performance sports having a lot of coffee or energy drink sloshing around in you as you try and push your performance limits is not ideal.
Will the strips do what they are claimed to do?
Probably not. Some drugs are given so that you hold them under your tongue and dissolve /adsorb them in the mouth. But this is usually for drugs that are rapidly removed by the liver before they have a chance to reach the general circulation. Drugs such as caffeine, where most of the drug reaches the circulation after being absorbed by the gut, show very little benefit if any from being absorbed via the mouth.
While the absorption begins earlier in the mouth, and the tissues of the mouth are rich in blood vessels, the skin of the mouth is less easily penetrated by drugs compared to the lining of the gastrointestinal tract. Also, the GI tract has a much greater surface area compared to the mouth, so there is less absorption potential.
Compared to caffeine tablets, the strips will be absorbed more quickly, but compared to coffee and colas, strips are absorbed only marginally faster.
But, surprisingly, while you may get caffeine in a little bit more quickly with caffeine strips, you may actually absorb less. Comparing caffeine containing chewing gum (not strictly equivalent, but the only published work is on chewing gum) to tablets and colas, there is much less caffeine being absorbed (less than half when comparing 50 mg doses delivered by chewing gum compared to a tablet). This may be due to swallowing caffeine laced saliva before it can be absorbed by the mouth, so the concentration is smeared out.
As well, studies that have looked at sports performance enhancement using gums delivering higher concentrations of caffeine (100 mg) than these strips have shown no significant improvement in endurance exercise.
Are They Safe?
They should be safe for healthy adults with normal metabolism. The strips are supposed to be consumed one at a time. For comparison, I’ll list the strips caffeine levels with representative levels of a variety of caffeinated beverages per typical serve.
One Caffeine Strip: 40 mg caffeine 375 ml Iced Coffee: 68 mg caffeine Average espresso: 75-85 mg Caffeine Instant coffee: ~ 65 mg Caffeine Tea: 50-80 mg caffeine Colas: 30- 70 mg caffeine Energy Drinks: 80-160 mg caffeine
Clearly, ingesting one strip will give you less caffeine than drinking a cup of average tea, let alone a decent espresso. And it won’t taste anywhere near as nice.
If you were to consume the entire packet, which would give you a total intake of 200 mg of caffeine, would that push you into undesirable effects? In healthy people, probably not.
Excessive ingestion of caffeine is associated with Caffeine intoxication and higher doses with Caffeine toxicity. The question being, what is an excessive dose?
What do we define as excessive?
Taking more than 300 mg of caffeine in one go can result in Caffeine Intoxication (DSM-IV 305.90). The symptoms of caffeine intoxication may include restlessness, nervousness, excitement, insomnia, flushing of the face, increased urination, gastrointestinal disturbance, muscle twitching, a rambling flow of thought and speech, irritability, irregular or rapid heartbeat, and psychomotor agitation.
But not dehydration, caffeine does not dehydrate you.
In a study of people who were admitted to emergency wards in NSW after drinking energy drinks, the commonest symptoms seen were palpitations/tachycardia, tremor/shaking, agitation/restlessness and gastrointestinal upset. The median caffeine consumption here was 400 mg.
For a normal, healthy individual with no heart disease or a mutation that reduces the livers ability to break down caffeine, and who has a modest level of coffee/tea/cola intake normally, consuming a whole packet of strips is unlikely to do too much to you. Intakes of between 100-200 mg caffeine are commonly used by athletes as performance enhancers.
On the other hand if you consumed a whole packet of the strips and washed it down with two 80 mg caffeine-containing energy drinks you would have a good chance of showing signs of caffeine intoxication (assuming that all the caffeine dose was absorbed properly, as discussed above, it probably won’t be).
How much caffeine is lethal?
Caffeine toxicity is seen with caffeine ingestion on the order of 1-2 grams caffeine, this is typically seizures or severe heart palpitation. You would need to consume 5 boxes of strips to reach these levels.
Actual death should only be seen with intakes of 5-10 grams of caffeine in one go (this is where you would need to drink 140 cups of espresso, over 100 cans of energy drink or 5 boxes of strips to kill yourself).
Standard strip consumption, even with energy drink usage, would be unlikely to produce true toxicity in healthy people.
However, if you have significant liver disease or a mutation in the enzyme that breaks down caffeine or are on certain drugs such as fluvoxamine, the liver enzyme responsible for the metabolism of caffeine is reduced or blocked, so toxicity can occur at much smaller doses.
The man who recently died after eating 12 caffeine containing mints (consuming about 1 gram of caffeine, theoretically below the lethal level) had cirrhosis of the liver.
Heart disease can also predispose you to toxicity, in Western Australia, a 25-year old woman with a disease of her heart valves died after consuming a solution containing around 10g/L caffeine.
Abuse potential:
While ordinary folk will be unlikely to be consuming a whole packet of strips and washing down with energy drinks, there is substantial risk that athletes will abuse them. There have been reports of Australian athletes consuming numbers of caffeine pills and washing them down with energy drinks, so the potential is there.
These kinds of consumption could easily produce caffeine toxicity; ironically, these high levels of consumption provide no performance benefit.
How much caffeine should people take?
A difficult question, with no clear agreed answer. Healthy, non-pregnant adults should limit themselves to consuming less than 500 mg caffeine in 24 hours (300 mg/day is considered moderate intake), and less than 200 mg in any single dose (typically the warnings on many energy drinks suggest you consume less than 200 mg / day, while some caffeine tablets recommend less than 600 mg/day). Pregnant women are recommended to limit themselves to less than 200 mg caffeine per day.
What is the best limit for children is poorly understood. A recent survey in the US showed that children ages 2–11 consume 0.4 mg caffeine/kg body weight and those ages 12–17 consume 0.55 mg/kg compared to the average adult caffeine intake of approximately 1.3 mg/kg. But what this means in terms of safety is unclear.
One study recommended that 3mg/kg body weight be used as the adverse event level for children. This means that an average 10 year old child could potentially consume 2 of the caffeine strips, just over the caffeine concentration in a 375 ml iced coffee, before we got seriously worried.
For adolescents (say 11-18) the American Academy of Paediatrics has recommended that they consume less than 100 mg caffeine/day.
The issue, as I mentioned in the interview, is the possibility that a young child could consume all of the strips (getting a dose of 200 mg or about 6 mg/Kg body weight for a 10 year old child, double the AAP limit). This would certainty result in the symptoms of caffeine intoxication, but, unless the child has other health issues, unlikely to result in true toxicity. This would be small comfort to a parent whose child is undergoing tremors, shaking and or heart palpitations.
While the strips do have clear warnings on the packet, children (and some adults) are notorious for not reading labels and the individual wrappings are unlikely to deter them.
The strips are being sold in newsagents, convenience stores and other venues where children go to purchase sweeties. If the strips are being sold near sweets, or ordinary chewing gums, the chances that kids will buy these strips are high. People selling these products should ensure that the strips are placed well away from ordinary chewing gums and confections, and make sure staff clearly understands the product should not be sold to children.
So bottom line:
Used by healthy adults according to the directions on the packet, these strips are unlikely to be a health risk, but nor are they likely to deliver a boost to sporting potential.
There is a risk that children will mistake them for sweets, and develop caffeine intoxication if they eat an entire packet.
There is abuse potential for athletes, as other caffeine containing drinks and tablets have been abused.
======================================================================== * for the past two weeks I’ve been doing an interview (TV, radio, print) on some aspect of caffeine approximately every two days. What is it about caffeine?