Compared with those who did not drink tea and coffee, drinking 2 to 3 cups of coffee and 2 to 3 cups of tea per day was associated with a 32% (HR 0.68, 95% CI, 0.59 to 0.79; P < 0.001) lower risk of stroke and a 28% (HR, 0.72, 95% CI, 0.59 to 0.89; P = 0.002) lower risk of dementia. Moreover, the combination of coffee and tea consumption was associated with lower risk of ischemic stroke and vascular dementia. Additionally, the combination of tea and coffee was associated with a lower risk of poststroke dementia, with the lowest risk of incident poststroke dementia at a daily consumption level of 3 to 6 cups of coffee and tea (HR, 0.52, 95% CI, 0.32 to 0.83; P = 0.007).
I think studies like this tend to overlook selection bias. What is typically omitted is that there is some degree of “tolerance” that’s needed to consume moderately caffeinated beverages. Individuals might avoid these drinks if they feel like they get negative effects (ie anxiety, palpitations, headaches) from them.
I know this barely scratches the surface of the uncontrolled factors, but I wanted to throw this point out there.
Also, are they the same mechanism? We know that staying mentally active can delay dementia symptoms for decades.
Could it be that people who do mentally taxing work for a living drink more tea and coffee per capita, especially as they approach a certain age, so that coffee and dementia are negatively correlated but not causal?
Anecdotal, but I drink water, coffee, and tea almost exclusively. I maybe have one soda a month, and it's typically one of those 8oz jobbies, and typically with pizza, and typically only because it goes so well with pizza.
"estimate the associations between coffee/tea consumption and incident stroke and dementia, adjusting for [...], consumption of sugar-sweetened beverages"
As is never highlighted, especially in media, is that it's relative risk reduction. Going by their study (and simplifying for argument's sake), there were 10k strokes out of 365k subjects, so <3% risk. A 30% risk reduction means now you're at 2% risk, so figure out whether that's worth adding coffee and tea for.
A <1% death rate was enough to cause the lockdowns in 2020.
If the media ran this endlessly, saying you'll have 30% less chance of stroke or dementia if you drink coffee and tea, people would probably panic on that too.
A large enough uptick in strokes at some point will, yes, but I don't think coffee/tea consumption will have that effect, plus our current consumption clearly _doesn't_, while Covid clearly _does_. (At least where I live, ICU's were previously not overrun due to anything)
It's not a spin, it's just the daily struggle of the health care system right now. I see no other solution but to take that seriously.
That doesn't mean we should take this study as serious just because it discusses something that may lead to something that, by itself, with a theoretical (large enough) uptick would overrun the system too.
Strokes are not contagious and do not spread exponentially through a population, overwhelming the health care system all at once. Things like smoking and lung cancer, or lifestyle related metabolic disorders might cause a lot of health care cost down the road, but they don't cause highly synchronized hospitalization throughout the population.
Some hypothetical, stroke-causing, meme-like behavior which can spread rapidly would have to be quite insidious to spread as effectively as COVID-19, cause a temporally correlated medical event, and not be self-limiting. The closest I can think of, off hand, are spikes in drug overdoses or things like suicide clusters. But those are examples are self-limiting, in that most people seem to recognize that they do not want to have that outcome.
That seems to depend on the typical duration of stay of a stroke patient in the various departments (emergency, ICU, general in-patient). I'm not familiar with stroke treatment, but from anecdotal exposure in my extended family's experience, they did not result in extended ICU stays.
That <1% death rate is only with every serious infected getting adequate care. If the disease went further out of control and intensive-care, oxygen etc. was no longer available it would be much higher.
Right, but the point that parent was making is that rather than just not implicating tea/coffee in causing these, the study shows that it reduces the chance of these.
That it's a relative risk reduction is not particularly relevant to that.
That said, I do agree that changes in relative risk are confusing and/or misleading to many people. A more interesting way of presenting this data, IMO, is the "number needed to treat", that is in order to reduce 1 stroke from occurring, ie, roughly 120 people need to drink 2 cups of coffee/tea per day to reduce 1 stroke, based on the numbers given here. This is obviously a lot more than the naive "30% means roughly 1 in 3 would see improvement" interpretation that the headline number pushes you towards.
Well, that’s the conclusion the authors want you to draw.
IMHO, that’s a higher burden of proof than a correlation study like this can offer.
As in, if I didn’t already drink coffee, and I was worried about stroke, I don’t think this study would be enough to confidently prescribe coffee as a stroke-prevention tool.
But if I do drink coffee and I am worried about stroke, this study makes me a little less worried, because the answer to “well did coffee-drinkers disproportionately get stroke?” is “no.” The fact that it goes the other way just makes it a stronger “no”.
Reasonable people could differ in interpreting this.
Hyperbole aside, I experienced the exact same sequence of events on this side ^_^
The conclusion, for those of you that are wondering:
> We found that drinking coffee and tea separately or in combination were associated with lower risk of stroke and dementia. Intake of coffee alone or in combination with tea was associated with lower risk of poststroke dementia.
It's my understanding that caffeine doesn't have a diuretic effect on chronic users with a tolerance for caffeine. IOW if you drink a few cups of coffee every day, it isn't dehydrating you; but if you don't usually drink coffee and drink a few cups in quick succession, it will have a diuretic effect.
caffeine irritates the bladder, inducing urination (often urgently). But the total amount of liquid expelled after drinking coffee is not higher than after drinking an equivalent amount of water. In this sense it is not a diuretic and does not dehydrate you.
Separately, enzymes in the coffee bean (not caffeine) also act as a peristaltic.
As someone with poor sensitivity to coffee, I’ve always wondered if these studies actually dismiss the possibility that people who drink coffee are people who can stand it, and as such have stronger hearts or something, and this it’s not a consequence of drinking coffee just a correlation.
Or that it is that frequent coffee and tea drinkers have a higher liquid intake per day or that it’s a socio-economic thing and people who cannot afford these are more at risk, …
All the study claimed was an „association“, nothing more.
This is a common concern in virtually all clinical studies and it's unlikely the researchers just ignored this. In principle these studies attempt to decorrelate confusing factors; from the abstract:
> We used Cox proportional hazards models to estimate the associations between coffee/tea consumption and incident stroke and dementia, adjusting for sex, age, ethnicity, qualification, income, body mass index (BMI), physical activity, alcohol status, smoking status, diet pattern, consumption of sugar-sweetened beverages, high-density lipoprotein (HDL), low-density lipoprotein (LDL), history of cancer, history of diabetes, history of cardiovascular arterial disease (CAD), and hypertension.
It's extremely difficult to do this in practice because people lie, there are other factors they might have missed and so on.
The controls give you information about confounders, but it still says nothing about the causal direction.
Typically the easiest way to turn it around is to switch where the authors chose to place the word "risk" and see if the new statement (with some appropriate changes, and adding "predisposition" to account for future events) still makes sense.
E.g. Predisposition to dementia lowers lifetime "risk " of coffee consumption.
The interesting thing is that assuming that there is a confounding variable that correlates with coffee consumption which is the real cause of the effect, the correlation can still be useful in some contexts.
For example, while that would mean that simply increasing coffee consumption wouldn't directly lower your risk of dementia and stroke, we can improve our assessment of the risk of a certain patient developing these conditions by asking whether they consume coffee. Even though the coffee isn't the cause, since it correlates with the cause, we still get information by doing that.
I plan to read more to understand their robustness controls, instrumental variable or other control strategy, etc. for causal inference. This said, they do control for many of the factors one would expect. From their Covariates section:
> Covariates
> In the present study, the selection of covariates based on (1) demographic variables, including sex, age, ethnicity background, education level, and income; and (2) a priori knowledge of potential confounding factors associated with incident stroke and dementia [30,31]. Covariates were documented including sex, age, ethnicity (White, Asian or Asian British, Black or Black British, and Other ethnic group), qualification (college or university degree, Advanced [A] levels/Advanced Subsidiary [AS] levels or equivalent, Ordinary [O] levels/General Certificate of Secondary Education [GCSE] or equivalent, Certificate of Secondary Education [CSE] or equivalent, National Vocational Qualification [NVQ] or Higher National Diploma [HND] or Higher National Certificate [HNC] or equivalent, other professional qualifications, or none of the above), income (less than £18,000, 18,000 to 30,999, 31,000 to 51,999, 52,000 to 100,000, and greater than 100,000), BMI (<25, 25 to <30, 30 to <35, and ≥35 kg/m2), smoking status (never, former, and current), alcohol status (never, former, and current), physical activity (low, moderate, and high), consumption of sugar-sweetened beverages, history of diabetes, history of coronary artery disease, high-density lipoprotein (HDL), low-density lipoprotein (LDL), and diet pattern (healthy and unhealthy, healthy diet was based on consumption of at least 4 of 7 dietary components: (1) fruits: ≥3 servings/day; (2) vegetables: ≥3 servings/day; (3) fish: ≥2 servings/week; (4) processed meats: ≤1 serving/week; (5) unprocessed red meats: ≤1.5 servings/week; (6) whole grains: ≥3 servings/day; (7) refined grains: ≤1.5 servings/day [32–35]) (S1 Table).
> Information on cardiovascular arterial disease (CAD) was derived from medical records (ICD-10 codes I20 to I25). Diabetes was ascertained on the basis of medical records (ICD-10 codes E10 to E14), glycated hemoglobin ≥6.5%, and the use of antidiabetic drugs. Hypertension was defined as systolic blood pressure (SBP) ≥140 mm Hg or diastolic blood pressure (DBP) ≥90 mm Hg, use of antihypertension agents, or medical records (ICD-10 codes I10 to I13 and I15). Cancer was identified through linkage to the National Health Service (NHS) Central Register (ICD-10 codes C00 to C97).
There are genetic variants associated with coffee consumption[1] so you're right, in a sense the groups are self selecting. It still could be the coffee and tea though, this kind of study could be the first step to looking deeper and finding out.
As others have mentioned, there's the metabolism bit, but as someone who's gone back and forth between decaf and regular, when you're not accustomed to caffeine, there's a bit of uncomfortablness that comes with the added energy. If I keep going and rebuild the tolerance, it goes way.
I think this is an interesting line of thinking. I was thinking along the same lines. I think it's probably the 'or something'. It's difficult to imagine what that would be exactly.
coffee sensitivity is due to an enzyme difference, not anything cardiac-related. the enzymes in coffee-sensitive people break down caffeine more slowly, prolonging its effect.
Can confirm - coffee sensitive. If I have a coffee at 11am, my heart rate will rise to 110 and stay there until I go to bed, before slowly declining overnight.
Discovered the gene thanks to consumer genetic testing, and the heart rate thing with a fitbit. I'm more careful these days.
That's what I do personally, I only consume decaf (and maybe once a month I'll dare drinking coffee and regret it after). People make fun of me, but I like the taste of coffee and I don't want to have a heart attack from drinking it :)
> We found that drinking coffee and tea separately or in combination were associated with lower risk of stroke and dementia. Intake of coffee alone or in combination with tea was associated with lower risk of poststroke dementia.
Beyond this, there are so many other health benefits to reasonable coffee/tea drinking. It's one of the few addictions that probably ends up being good for you.
>It's one of the few addictions that probably ends up being good for you
I thought that for a long time, until I realized that afternoon caffeine was correlated with my inability to fall asleep at night. Cutting coffee (even dark chocolate) after lunch has greatly improved my sleep quality. Still love it in the mornings though.
I'd usually aim for drinking the first coffee/tea about 1-2 hours after waking (it is important to wake up by circadian rhythms to get the best effect) and drink the last beverage around 2pm, or at latest 3pm.
Haha.. Yes it's obvious in hindsight. I think a few factors played into it.
First was an underestimation of the half life of caffeine. It stays in your system for a while, and stacks when you have multiple throughout the day.
Another was my personal sensitivity to caffeine with regards to sleep. I know many people who can't drink coffee at all and others who can drink it as a digestif. I'm somewhere in the middle.
The last is being embedded in a coffee-drinking culture, without personal awareness of the above two points. So I would drink it later than I should with people who didn't (or didn't know they) have a problem drinking it at that time.
While there are thousands of "herbal teas", just "tea" refers to beverages made with the Camellia sinensis plant. See https://simple.m.wikipedia.org/wiki/Tea
There are also lots of different cultivars of that plant and different ways of treating the leaves. Since they all taste different, one would have to assume that the chemical cocktail the brew contains is also markedly different. Whether or not that has an influence on the purported health benefits is unclear.
I suspect the maturity and processing of the leaves have more of an effect than the cultivar.
If this effect is being observed in both coffee and tea, my guesses would be it's either caffeine, something with the roasting, possibly fermentation (but I'm not sure if all tea is fermented), something with fluid consumption, or something with the mental ritual of drinking mild stimulants.
There is a single tea plant, grown in different regions, harvested at different times, and processed in different ways to white, black, green, matcha and pu err tea. I would presume there is no massive difference from the health side as they are largely the same. If in doubt get an organic green tea as green tea best preserves vitamines.
Then there are infusions of fruits, leaves, etc which are not strictly tea.
And there are the above teas with other plants or oils mixed in (e.g. jasmine flower, bergamotte, ...). As long as you don't add much sugar I doubt these have much different impact unless these are plants with known effects of their own (ginseng, ginko, lemongrass, ...).
Black tea applies to Europe as a whole as far as I can tell.
Which parts of the world prefer green? Chinese and some Asian restaurants here (Poland) feature green tea quite prominently, but that’s the limit of my experience.
Tea has more caffeine than coffee but it has l-theanin which calms down its effect, by combining l-theanin (green tea extract) with coffee you can enjoy it without side effects no abnormal heart rhythm, no anxiety-like feelings etc.
Interesting - I'm wondering if both tea and coffee intake is just a proxy for people having cushy office jobs who therefore are less exposed to toxic substances over their lifetimes than others who work in non-office settings.
My grandfathers were a coal miner and a steel miller. Lots of coffee was consumed on/around the mines and on breaks in the mill. The image I have of both of them going off to work includes them carrying a silver or green painted Thermos bottle.
I see results popping up from time to time that caffeine is good for cardiovascular health. That makes intuitive sense to me - since a big benefit of aerobic exercise is getting your heart rate up, caffeine should have some of a similar effect. This might be particularly strong in the demographic susceptible to strokes and dementia, as they are less likely to be exercising in the first place.
Then, I wonder if better cardio health removes one stress factor causing these diseases.
Not remotely a biologist, and heavy coffee drinker.
factories invented the coffee break to increase worker productivity on long shifts (so Michael Pollan says), it is not a habit exclusive to white collar work.
In my personal unscientific opinion, I am observing complete opposite - coffee is the modern evil of our society.
My gut feeling is telling me that coffee and digital devices are responsible for big parts of the population suffering from mental illnesses, caused via chronic sleep deprivation. Of course majority of those mental illnesses are under reported - being sleep deprived for months does not make you bipolar maybe, but depression can and does happen (as well as myriad of other issues).
There are too many studies who show relationship between sleep and all kinds of illnesses (majority - mental), and nobody can argue that coffee is NOT responsible for that at least partially.
When I recently quit on coffee, I had such strong withdrawal symptoms, I was unable to function for 4 days. I had strong headaches and was almost vomiting.
No study will convince me this is a good/healthy thing for a human body. It is drug which is so omni-present, if you look around it is scary.
> being sleep deprived for months does not make you bipolar maybe, but depression can and does happen
It shaves off 10 to 20 IQ points in me when I'm on a bad streak. I have failed FAANG interviews because of bad sleep. I still probably would've failed them, but it'd have been much closer. I literally remember one coding interview where I was thinking "if I just had enough sleep, I'd have a solid shot" (the other coding interview was so easy I could even do it in my half-ragged sleep-deprived state).
It's funny you should talk about sleep deprivation messing with your mind... I once remember trying to program a for-loop in C# about 8 or 9 years ago (I've been programming since the 90s) when my son was a baby. He'd been up and down for a couple of days as he was unwell and my sleep-addled brain wouldn't let me create a for-loop.
No matter what I tried I could not get the code to compile.
I still laugh about it now but it definitely highlights the importance of sleep.
Coffee does not really affect my sleep. I know this for 2 reasons:
1. I periodically go off coffee, for various reasons, but frankly never notice much difference to my sleep quality.
2. I have 2 kids that deprive me of sleep much more effectively. Or, put otherwise, no matter how much I drank during the day, I fall asleep like a log. And then it's not coffee disturbing my sleep, but crying children.
I can see though that coffee abuse _could_ lead to sleep deprivation and related issues. But it's like alcohol could lead to alcoholism, but doesn't have to. Though, incidentally, apparently deliberate sleep deprivation is one method of tackling depression - so it's not all bad.
Please look up studies by Mathew Walker. They did numerous studies with people claiming coffee did not affect their sleep. What they found was while those people would fall asleep, and sleep throughout the night, the quality of the sleep (i.e. minutes in deep sleep) was substantially worse.
But I agree that abuse is what is causing majority of the problems (and it was in my personal case)
My confidence in Matthew Walker was enormous after reading "Why We Sleep", then dropped to around 0 since reading this: https://guzey.com/books/why-we-sleep/
A lot of it doesn't require any domain knowledge to verify.
Doesn't change the information in his book about how it is genetically determined how quickly you digest the caffeine. My dad can easily have a coffee around 19:00 and still sleep well, while when I have a coffee in the afternoon I will have big trouble sleeping.
The alleged failures in "Why We Sleep" go as far as quoting papers and books claiming they say "X", where in fact they claim "not X". So to me, Walker saying or quoting something bears 0 informational content (almost).
But different rates of caffeine tolerance and digestion certainly conform with my personal observations, Walker or not.
> apparently deliberate sleep deprivation is one method of tackling depression
Briefly and temporarily, but efficacy quickly drops off with near-term repetition. As (apparently) with psychedelics, it's good for a temporary change of perspective that can be leveraged with the right techniques into lasting improvement, but much more of an adjuvant to therapy than a therapy in its own right.
I, too, am curious about the negative effects of coffee (or caffeine, rather). The potential positives are well known through many studies like the OP, but it is also well known that caffeine triggers a stress response (increased adrenaline, cortisol). We know that stress, beyond a short burst, is detrimental to health.
There seems to be a wide variety in different people's caffeine sensitivity, but for me, a coffee habit leads to a downwards spiral that ends with permanent tension and migraine episodes. I have tried this cycle enough times by now to know the cause and effect. I have to wonder what other effects the continued stimulation of caffeine has.
Sensitivity varies wildly for for different people. I seem to have a very low sensitivity - the only time I have felt the effects was on a barista course where I think I was up to 6-7 double espresso shots in the 90 minutes.
I drink espresso in the morning, black coffee through out the day and stop before dinner. It's around 4-8 mugs every day. On holidays I often go a days without any coffee for various reasons with no ill effects. I have gone an entire month substituting coffee with water to test the hypothesis that it doesn't really affect me and I felt no different. HR, BP, sleep quality, tiredness, mental performance, digestion all remained stable.
My neighbour gets a headache if he skips coffee for a day.
I like to think people can decide to kick coffee for themselves if they actually suffer from sleep deprivation.
I for one have coffee in the mornings and stare at my phone until I fall asleep, and I sleep like the dead at night. But, that's purely anecdotal.
I don't think people will listen to others saying 'stop drinking coffee!' or 'stop looking at screens!' if they don't actually have problems. On that note, one shouldn't start self-medicating with sleep hormones (currently available over the counter) to try and optimize their sleep. If you have to force yourself to sleep so you can min/max your day, you're heading to a crash and burnout.
Your experience suggests that your level of coffee intake may have been excessive.
I abstain from coffee (normally eight cups daily) and alcohol (normally three bottles of beer weekly) for a two-week period as a prescription against chemical dependency.
Typically this results in one day in which I am more irritable, nothing more.
Any consumptive habit can be evil in the absence of moderation and discipline.
Ok regardless of conclusion life is too short to give up grinding beans, extracting coffee from them and drinking it. Glad it’s “good for you” in this study.
don't want to give up grinding beans, but I want to find an alternative to jamaican blue mountain so that my wallet stops complaining. Everything else seems hyper sour and acidic by comparison.
I paid £24 for 250g of Blue Mountain a few weeks ago. Unimpressed - it tasted like - er - coffee. I mean, it was like regular coffee, a bit smoother than usual.
So I've gone back to my touchstone brew: Harar Hyena (it's from the Harar region in Ethiopia; the "hyena" bit is because the town is famous for being infested with hyenas). It costs half as much. I was warned the first time I bought it that it's not to everyone's taste; well, it's certainly to mine. It's fruity and complex. I certainly wouldn't describe it as acidic.
I can't write tasting notes, I can't bear to be that pretentious; but The Spruce Eats says: "This flavor is often described as fruity and winey with a mocha note, medium acidity, and a full body."
James Hoffman has a video about tasting coffee for yourself. Basically looking at acidity / bitterness / body / strength / sweetness. Rating out of 5 kinda things. Always comparison based and
using cupping. (I have not done it yet but I’m going to treat myself to some barista training. It’s actually very affordable thing to do)
Then pick out any comparisons that come to mind but don’t think too hard about “is it a strawberry or raspberry”. Doesn’t matter. Whatever comes to mind. I can’t even pick fruits is just think “acidic, sweet”
The purpose, rather than to sound sophisticated is to get an idea of what coffee you like.
For me a dark roast and chuck in some milk can’t be beaten, but it’s interesting trying the fruity stuff. And when I say fruity … it ain’t subtle like wine. Some coffees taste like tea!
The thing I like about blue mountain is a strong coffee flavour, very smooth, without any acidity or sourness. That's what I value from it. I'm not looking for fruity acidic or sour because I don't like any of those things. I'm looking for smooth bold coffee flavours without those things.
You can enjoy your coffee that you enjoy. I certainly wouldn't, but I'm glad you do.
In my experience all the etheopian coffees I've had were unacceptably sour. But taste is personal and you are free to enjoy it.
Until quite recently it was still cheaper for me to be drinking blue mountain than it was to be using those keurig pods. I just have decided to spend less on coffee in general, but haven't found anything to replace the blue mountain or even approximate it.
tasting notes don't have to be pretentious, they are about distinguishing coffees when tasted side by side -- not for going deep into the made-up subtleties about what minute flavors are present if you brew a single cup.
usually they are hiting flavor compounds that are in the coffee. in the example you gave, knowing what usually make it into coffee:
fruity i associate with citric acid.
winey is probably acetic acid.
mocha is the classic chocolate flavor of the maillard reaction from roast and bitterness
Minor exception: "Exotic" fruits like mango or pineapple may mean there are fermentation flavors present, e.g. with naturally processed beans (vs washed process).
yeah, good point. have you heard of the podcast Making Coffee by Lucia Solis? it's really good on the topic of coffee fermentation, and she addresses those fruit compounds in particular because it's considered a defect in wine but she grew up eating papaya so enjoys the taste.
Wow, that cookie prompt had such a dark pattern that it destroyed any credibility. I had to scroll down past multiple feet of blank space to get to the "accept my cookie choices" button, while the "accept all cookies" was visible from the start. Very scummy.
Filtered or unfiltered ground coffee? I recall other studies that correlated protection or risk of cancer with coffee to different studies with different cultural groups, and noticed that the studies showing negative effects where all cultures that typically drank unfiltered coffee. Which, as an instant coffee drinker, left me in the dark. This study does check type of coffee, but does not differentiate filtered or unfiltered ground coffee. Not that it helps me, as I think I need another coffee before I can make sense of the instant vs. ground comparisons (first reading it seems contradictory, so I'm assuming I'm misreading or missing some nuance).
I haven't read the whole doc but does it take into account stress or factors that lead to stress?
For example, money problems, dangerous job, working in toxic environments etc.
I reckon we don't put enough "science" into working out the life-extending properties of a non-toxic job and a health bank balance.
FWIW I was diagnosed in September as having stable angina. I eat really healthy, don't smoke or drink, no family history of heart issues, and all my blood work was great. However, I have been under immense stress for the last two years to the point of sleepless nights etc (won't go into the details).
Sweet. Strokes terrify me. Supposedly ubiquinol and citrus bergamot help prevent them, but I haven't researched deeply enough to make up my mind about it.
From what I can see, the research method is quite flawed.
What if drinking more coffee or tea makes you die younger? This would result in the same data they base their conclusions on.
E.g. dementia en strokes correlate with age. If you die young because of high coffee consumption you wouldn't show up in the "drank coffee and subsequently had a stroke" group.
The issue with research and the internet can be boiled down to singular dimissive comments like this. You see them especially a lot on Reddit.
This is a prospective cohort study - it is not meant to cover all limitations. Every scientific study will have strength and weaknesses, an RCT won't ever have 350 000 participants. Studies with large sample sizes almost always have to resort to either self reporting or interviews in order to collect at least some of the data.
You're not meant to take an individual study's results as the truth - it's the overall body of research that's important. When you see the same or very similar results from studies with varying study designs from different populations done by different researchers with different methods the results become more credible.
Though this specific study is notable as the effect size is quite large, the bias from self reported coffee or tea intake would have to be quite large itself to remove it.
And with regards to coffee and tea consumption and research, this is a pretty well researched area already, and the general consenus is that consuming tea or coffee does have health benefits.
Compared with those who did not drink tea and coffee, drinking 2 to 3 cups of coffee and 2 to 3 cups of tea per day was associated with a 32% (HR 0.68, 95% CI, 0.59 to 0.79; P < 0.001) lower risk of stroke and a 28% (HR, 0.72, 95% CI, 0.59 to 0.89; P = 0.002) lower risk of dementia. Moreover, the combination of coffee and tea consumption was associated with lower risk of ischemic stroke and vascular dementia. Additionally, the combination of tea and coffee was associated with a lower risk of poststroke dementia, with the lowest risk of incident poststroke dementia at a daily consumption level of 3 to 6 cups of coffee and tea (HR, 0.52, 95% CI, 0.32 to 0.83; P = 0.007).