Category Archives: Evidence

Homeopathic harms vol. 8: Opportunity costs

The excellent Nightingale Collaboration published some figures lately on how much the NHS in England spends on prescribing homeopathy. The figures are publicly available (and linked via the Nightingale Collaboration post), and represent every prescription for homeopathy dispensed by a community pharmacist – anything provided in a homeopathic hospital (or ordinary hospital, though I’d hope that doesn’t happen too often) wouldn’t show up.

You should go and take a look at that post because it’s interesting to see how prescribing has changed over the last 15 years or so.  It did make me wonder though, what is the opportunity cost of all this homeopathy? That is, what opportunities have we lost because we spent that money on homeopathic treatments? These opportunity costs represent one more indirect harm of the continued use of homeopathy.

I accessed a few resources to see what the score is.  Those resources are all publicly available, so you can (and should) double check my workings. I used:

In the 2013 calendar year, the NHS paid £137,000 for homeopathic remedies dispensed in community pharmacies.  By my calculations, that’s enough to pay for:

  • Wages for six newly qualified nurses, dieticians or radiographers or
  • Wages for five specialist nurses or
  • Twenty-six hip replacements (without complications) or
  • Twenty-four knee replacements (without complications) or
  • Delivery of ninety-one babies or
  • One hundred and ninety-six cataract operations or
  • Four hundred and fifty-nine MRI scans

(All numbers are rounded down, since it’s pretty hard to employ 0.4 of a person or replace three-quarters of a hip. Staff are assumed to be at the bottom of their pay band, which is probably a bit optimistic.)

Those numbers might not seem like much, but once again it comes down to cost/benefit analysis.  The best that we can hope that those homeopathic prescriptions achieved was some kind of comforting placebo effect for the patient.  Six nurses, even spread out around the country, could achieve an awful lot more than that.

Green tea and beta blockers

The BBC published an article a few days ago titled “Green tea ‘can impede nadolol blood pressure medicine’” It represents some pretty sloppy health reporting. Let me expand, bit by bit.

Green tea can weaken the effects of a commonly prescribed blood pressure pill, experts warn.

We’re off to a bad start. Right from the first sentence of the article, we have a glaring error.

The drug in question is called nadolol, which is a beta blocker from the same family as atenolol and propranolol. The chances are you’re familiar with one of those drugs, but not with nadolol, and there’s a very good reason for that – nadolol is not commonly prescribed as claimed by the BBC. In fact, it’s barely prescribed at all. The evidence for that is publicly available; the Health and Social Care Information Centre (HSCIC) is a UK body which regularly publishes statistics on drugs prescribed in England. The latest set was published on the 4th of April 2013, and details everything prescribed in 2012 – an awful lot of drugs. You can get a copy for yourself here.

The HSCIC data tell us that in 2012 there were 32,355,600 prescriptions dispensed for beta blockers. Those figures include 11.5 million prescriptions for atenolol, 14 million for bisoprolol and over 3.5 million for propranolol. How many prescriptions for nadolol? Seventeen thousand. That means that nadolol accounted for 0.05% of all the beta blocker prescription items dispensed in England in 2012. I don’t think that 0.05% of anything can ever be described as “common”.
One important thing to note about the prescribing data is that it doesn’t tell you how much of each drug a prescription represents – some might have been for a four weeks supply, some might have been for 12 weeks. However to change the figures above, each nadolol prescription would need to have been for several years supply, which isn’t something that happens.

The next problem with the BBC article is this:

The study in the journal Clinical Pharmacology & Therapeutics found nadolol’s lowering effect on blood pressure was blunted in the 10 volunteers who agreed to drink green tea.

Ten volunteers. Ten. Volunteers. Neither of these words is good in terms of clinical research. If I were evaluating a drug and saw a trial with ten people in it, I would only take the evidence into account if there was no larger, randomised trial available. In fact, if a trial in ten volunteers was the only available data I still might not read it; my recommendation would be along the lines of “we do not know enough about this drug to use it safely; we need more evidence”. The burden of proof for a safety issue is clearly lower, so that’s not the best analogy, but the fact remains that the sample size is not sufficient for the level of fuss that’s been caused here. It’s also worth noting that these were *healthy* volunteers. How do we know that the same thing would happen to a person who was unwell and required a beta blocker?

Follow-up tests in the laboratory revealed that green tea blocked a drug transporter present in the lining of the human gut that helps move nadolol into the cells.

Well. Kind of. Follow-up tests were done in a laboratory, but not in human guts. The tests were done on cells, in a petri dish, on a cell line called HEK293, which were originally derived from Human Embryonic Kidney. Although they are kidney cells they’re probably not very useful for telling you what would happen in a living, adult kidney. It maybe doesn’t matter too much what the cells are as long as the drug transporter involved is the right one, but I’d expect more clarity from the BBC.

So the end result is that some scientists found that drinking green tea makes a drug that is very rarely prescribed work a bit less well, probably, in healthy volunteers. Let’s be clear: that’s a perfectly adequate conclusion for a scientific study – it’s tiny nuggets like this that are the building blocks of good medicine. The problem here is the quality of the reporting on the issue. Very little additional time, effort or words would have been needed to make the article much more representative of the real impact of the findings.

If you’re a regular green tea drinker who takes nadolol, the chances are that your dose has been adjusted to suit you already, through a process of your doctor checking your blood pressure and tweaking the dose. If you’re an occasional green tea drinker, you probably have nothing to worry about, but you can minimise any risk by leaving several hours between taking your pills and drinking any tea. It’s very important to realise that if there is any risk (and we can’t be sure by any means from a study of ten healthy people), it’s likely to be minimal. If you’ve any worries at all, have a chat with a local pharmacist or your doctor.

And the next time you see a story like this, don’t immediately take it at face value.

Edit: it’s worth mentioning that this study tells us nothing about other beta blockers. They might be affected in the same way, they might not – we won’t know until someone takes the time to do the experiments. If you’re concerned about a drug other than nadolol, and your habits haven’t changed lately, it’s unlikely you have anything to worry about. If you have any worries at all, your pharmacist or doctor will be happy to discuss them with you.

Why you can’t believe weight loss testimonials

I wrote yonks ago about why you can’t always beleve the hype about fitness fads, and encouraging people to think critically before buying in to anything. At this time of year a lot of people are making themselves promises about the way they look, so when I stumbled across a short blog post this evening, I thought it was worth sharing.

The post illustrates exactly how easy it is to fool the eye (and the wishfully-thinking brain) with just a little work on posture, flexing the right muscles, using good lighting and a touch of post-production work. Just take a look at the panel below – all of the images in it were taken within the space of an hour. With a few changes of outfit and a quick shave, the author was able to take a series of photos that any fitness “guru” would be proud to use as a before/during/after montage (click on the image to view a bigger version, click here to read the blog post in full).

So what’s my point? When it comes to fitness, don’t believe your eyes. Don’t part with your hard-earned cash on the basis of a flashy web page and a few beguiling words. The best way to assess these things is to find someone who knows what they’re talking about, and talk to them about it – social media is a great way to do this, as it gives you access to thousands of experts almost instantly. I’d be happy to help you start – just leave a comment or send me a tweet.

So you think you do Tabata?

I just found this post, fully-formed, in my drafts folder. I wrote it in April, which shows just how badly I’ve neglected this blog. Sorry about that, but to tide you over, have a little post on fitness. This post is shamelessly stolen from myself, from a totally different blog.  I’m re-posting it here because I think it makes points about critical thinking and evidence that fit with this blog’s ethos pretty well, and also carry on the theme of questioning what you’re told about health and fitness that I started a few weeks ago.  Without any further hesitation, here’s what to bear in mind when you hear the word “Tabata”…

I have a bugbear. I’m going to use it to hopefully produce a blog post that’s useful and informative, but first I’m going to get something off my chest.

If you work out regularly, or even if you don’t, the chances are you’ve heard of the Tabata protocol.  Named after Izumi Tabata, the chap who first published an academic journal on the subject, the protocol is very simple:

  1. 20 seconds of work, immediately followed by 10 seconds of rest
  2. performed 8 times without any pauses or interruptions, for a total of 4 minutes
  3. with the working phases performed at 170% of VO2max

If you deviate from this on any point, you’re not doing Tabata, you’re doing interval training.  You may even be doing High Intensity Interval Training (HIIT), but it’s still not Tabata.  Does it matter? Well, yes.  Just because you’re doing intervals on a 20:10 split doesn’t mean you’re working to the same intensity as the Tabata protocol, and that means you can’t necessarily expect to get the results of the Tabata protocol.  As an example, depending how hard you’re working it’s a little bit like the difference between doing a class like Body Pump, and training with Olympic weightlifting; both might make you sore the next day, and help you get stronger, but it’s evident that in the long-term, and arguably the short- and medium-term too, the results are very different.

That’s my pet peeve (more-or-less) off my chest, so on to the useful part.  Points one and two on the list above seem straightforward, but what’s VO2max?

Simply put, it’s the maximum volume of oxygen that your body is capable of using. It’s usually expressed in litres per minute (L/min), or in millilitres per kilogram of bodyweight per minute (mL/kg/min). Men generally have a higher VO2max than women, and it tends to increase as you get fitter (and also decrease as you get older).

The next obvious question is, if VO2max is the maximum volume of oxygen your body can use, how can you reach more than 100% of it? That’s because your body has two energy systems.  Let me expand

  • The aerobic energy system uses oxygen to produce energy. It uses glucose, which goes through a series of chemical reactions to produce energy molecules like ATP, with CO2 and water as the waste products, and a few other things that are important to your body (but not to this blog post).
  • The anaerobic system can produce energy in the absence of oxygen, by using up molecules like ATP, and by breaking down glucose and glycogen in the absence of oxygen.  This produces by-products like lactic acid.  Once you’re at rest, your body will use some of the oxygen it’s consuming to metabolise these by-products and return your muscles to peak condition.  This is sometimes referred to as the “oxygen debt”, because you’re paying back oxygen for energy you’ve already used.

What this means for you is that you can work at a rate that is higher than your VO2max; your aerobic system will consume as much oxygen as it can, and your anaerobic systems will also kick in, but you’ll have an oxygen debt to pay off once you’re finished.  Back in the 1990s Tabata decided to test what effect using both of these systems at once would have on fitness, so he took the now-familiar 20:10 protocol (which was already being used by the Japanese speed skating team in training) and compared it to steady-state cardio.

A summary of the results is available for anyone to read if they want to, but the gist of it is this:

  1. The study was quite small, with a total of 23 men who were already physically active – no women were tested. Only 7 men completed the interval training experiment.  All athletes trained 5 times per week in total.
  2. Athletes performing cardiovascular exercise at steady state (70% of VO2max) for an hour significantly improved their VO2 max.
  3. Athletes performing intervals of 20 seconds of work at 170% VO2max interspersed with 10 seconds rest (with one 30 minute session per week at steady-state 70% VO2max) increased their VO2 max by a similar amount to the other group, but also increased their anaerobic capacity by 28%. In reality this group performed 7-8 sets of high-intensity work in each session; the session was terminated if their pedalling speed dropped below 85RPM.  If they were able to do 9 sets, the difficulty was increased the next time. This means that the workout was always varying, and it’s likely both that no two men ever did the same workout, and that no man ever did an identical workout more than a few times.

One really important point to take away from all of this is that working at 170% of your VO2 max is hard.  Really hard.  Joe Bloggs can’t do it, at least not without falling over or being sick (or both). It takes a trained athlete, someone who pushes their limits most days to achieve this kind of intensity. And since this is the only protocol that was tested, this is the only protocol that we can make claims about.  Even them the claims aren’t particularly strong if you look at this trial in isolation – the results for seven men who were already quite fit aren’t likely to generalise very well to a larger population of diverse individuals. Crucially, if you work at less than 100% VO2max (which most people will), you certainly shouldn’t expect anaerobic benefits of this magnitude, if any.

So what was my point again?  A large part of this is my belief that language should be used accurately – call a spade a spade.  The Tabata protocol is a very specific thing, which has been found to produce very specific results.  Calling your workout Tabata when it’s not is at best pointless, and at worst misleading (or, if you’re a fitpro selling your services, false advertising).

There’s no doubt that doing almost any form of HIIT is beneficial  (and I don’t mean to discourage it), so please don’t stop doing it, but – to keep me sane – please do stop calling it Tabata?  Cheers 😉

Homeopathic Harms vol 5: interactions

I might be a little quiet for the next wee while due to some unforeseen circumstances,  but to tide you over here’s the next installment in the Homeopathic Harms series by @SparkleWildfire – interactions.

In the next installment of our series on the harms of homeopathy, I want to talk about interactions. I’ve covered this a bit in the past, but let’s have a look at this area in a bit more detail.

We all hopefully know by now that homeopathic medicines pretty much have no trace of active ingredient in them by now. Do we need to worry about drug interactions with homeopathic remedies?

Can homeopathic medicines interact with conventional medicines?
The obvious answer is no. Magic Sugar Water Pills are highly unlikely to affect any conventional medicines. There’s a lack of actual evidence to prove this, but I think it’s pretty safe to rely on a theoretical basis here. So that’s great, right, blog post over and see you later. If only it were that simple.

Read the rest over at A Healthy Dose of Skepticism.

Should you believe the fitness hype?

I see this over and over again among otherwise very intelligent people; an odd belief that the latest “big” thing in exercise or weight loss will be a magic bullet that suddenly brings them the body they’ve always thought they should have. Zaggora hot pants (Burn more calories!), Skechers Shape Ups (reduce cellulite!), green coffee extract (100% natural!) – the list is basically endless. Leaving aside the notion that this will somehow make them happy (for I haven’t the knowledge or skills to even begin to tackle that), why do these bright people fall for it?  I can’t answer that either. It’s potentially very harmful though – this tweet from @nchawkes says it rather well:

People end up spending frightening amounts of time, money and energy on these promises, and even when there’s temporary success (often due to diving into a new regime with a positive opinion, in my totally-un-evidence-based opinion) ultimately there’s stagnation at best, failure or regression at worst. These things are hugely destructive to body image and overall self-image.

So if I can’t explain the fascination with these things, the least I can do is provide a small extra weapon in the battle against profiteering and misinformation in the fitness world.  (Aside: it’s worth noting that much of the misinformation is spread amongst well-meaning friends, just trying to help one another; this type is just as difficult to address as any other dearly-held belief).

My first pearl of wisdom is hardly novel: anything that seems too good to be true, is. The cold hard truth is that you can’t permanently change your body without permanently changing your diet and lifestyle; they needn’t be massive, life-altering changes, but they must happen. You also can’t permanently change your body by throwing money at it instead of good quality food and exercise (unless we’re talking surgery; that’s pretty permanent).

My second piece of advice is: apply critical thinking. Is there something you’re naturally skeptical about, or distrustful of? Apply that same level of suspicion to diet and lifestyle advice. New device guarantees weight loss in one workout? Great. What’s the mechanism? Does it seem plausible? Is it more likely that it’s just helping dehydrate slightly, thereby losing water via sweat? Never ever forget that water’s heavy; 1kg (2.2lb) per litre to be precise. Doubt everything. 

Thirdly, and maybe most importantly (and predictably), demand evidence. Good quality evidence at that. Be ruthless. Be picky. Crucially, don’t accept anecdotes. These are everywhere in weight loss fads, to the point that I feel they’re worthy of a specially-adapted version of the anecdote rules:

  • Did the person gain the advertised benefit, and maintain it?
  • Was the advocated treatment the only one used?
  • If it’s really so good, why aren’t doctors and fitness professionals everywhere advocating it?

I’m hoping to look at some individual claims in more detail, but hopefully this post will at least serve as a cue to get you thinking about the way you look at claims in the weight-loss industry.

Homeopathic Harms Vol 4: OK, there’s SOME evidence

Last time I discussed the problem of missing evidence of harm in homeopathy trials and consequently in systematic reviews.  This time, I’m going to discuss some evidence of harm that we DO have. Sadly, it’s not comforting.

In December 2012, a systematic review of the adverse effects of homeopathy was published in the International Journal of Clinical Practice (aside: for a quick explanation of systematic reviews and adverse effects, take a look at volume 2 in this blog series).  The authors of this review searched five databases of medical literature totalling nearly 50 million published trials (though likely with considerable overlap), and found just 38 articles that discussed case reports and case series of adverse events with homeopathy.

It’s worth noting at this point that if systematic reviews are the pinnacle of the evidence pyramid, case reports and case series are somewhere towards the middle or bottom, depending who you ask.  They’re not ideal, because they’re not rigorous – they rely on someone not only noticing an adverse event and linking it to homeopathy, but taking the time to sit down and write about it and submit it to a journal.  Then of course they’ve got to find a journal willing to publish it.  If any of these steps don’t happen, there’s no published evidence for the rest of us to base our decisions on.  So if our systematic review found 38 published reports, the obvious question is “how many were never recognised, written up, or published?”  We’ll never know the answer to that.  Sadly in the absence of high quality reports of harm from the published clinical trials, this is the highest level of evidence we have.

Back to the review.  The 38 retrieved reports contained information relating to 1,159 people from all over the world.  Surprisingly, only 17 of the reports related to indirect harms – the results of substituting conventional care with homeopathy – although some of those indirect harms were severe.  Several people were admitted to hospital (including intensive care) due to replacing their conventional medicines with homeopathy, at least one was left with permanent effects, and one person died.

That leaves 1,142 people who suffered *direct* adverse effects as a result of using homeopathy.  This seems rather counter-intuitive, and I’m at a loss to explain to explain many of them given that your average homeopathic remedy contains precisely no active ingredient.  The authors of the review suggest that perhaps allergic reactions or ingestion of toxic metals (like arsenic or mercury) might be partly to blame.  They also suggest that low dilutions of remedies might be a potential source of adverse effects, but point out that the vast majority of these reports were associated with remedies at 12C potency or below.  To be clear, 12C is the dilution factor at which the chance of a remedy containing even one molecule of the original parent substance is effectively zero.

But whatever the mechanism, it seems clear that the review provides evidence of direct harm being caused by homeopathy.  Some of these harms were reported simply as “mild”, with no other details offered.  Some were potentially very distressing, like dermatitis, hair loss, and migraine.  Some were very serious indeed, including anaphylaxis (life-threatening allergy), acute pancreatitis, cancers, and coma.  Once again the consequences of the effects included hospitalisation, admission to intensive care units, and death.  For a treatment modality generally touted as totally safe, that’s a pretty alarming set of side effects.

So what can we learn from it?  There’s a valid argument to be made that there’s little point conducting more randomised controlled trials of homeopathy, because all of the good quality ones end up showing the same thing: no benefit over placebo.  But where more trials are conducted, we should be demanding that all adverse effects are collected and reported in the same manner as trials of new medicines.  Case series and reports are not proof of causation, but there is a bulk of evidence here that is concerning, and which should be addressed.  The best way to do that is in good quality trials.

In the mean time, is there anything else we can do?  Yes there is – in the UK at least.  The medicines regulator in the UK, the MHRA, runs the Yellow Card Scheme.  This is a mechanism by which anyone can report any side effect they experience after taking a medication.  I would strongly urge anyone who has suffered an adverse event after using homeopathy (or who knows someone who has) to visit  It’s quick and simple, and will help make remedies safer for everyone.  Similar schemes will be coming into effect throughout the EU soon, but if you live elsewhere please check and see if there’s anything similar.  We need all the data we can get!

Does homeopathy have a place in therapy?

Given the current blog series I’m collaborating on regarding the potential harms of homeopathy, I thought it might be useful to stop for a moment and discuss its appropriate place in therapy. Do I believe that informed, consenting adults should be able to choose homeopathy as part of a treatment regime? Yes.

Are most people fully informed, and therefore able to give full consent? No, I don’t believe they are.

If people are making their treatment decisions based simply on assertions like “it’s safe” or “it’s gentle and natural” or (worst of all) “it works for me”, they are not fully informed. (To see why “it works for me” isn’t adequate, take a look at my post on anecdotes). This creates an ethical problem that should be insurmountable for any decent healthcare provider.

The evidence in favour of homeopathy simply does not reach the standard that we demand of conventional medicines. The evidence that it has the potential to cause harms (as we are showing with the Homeopathy Harms blog series) is very real.  Does a patient tend to feel better after seeing a homeopath?  Probably.  In these days of seven minute GP consultations the chance to sit down for an hour with someone who wants to listen, and dig deeper, and really *help* you is probably a really lovely thing.  Should we mistake that for thinking that homeopathy is a beneficial discipline? No.  Should we allow double standards by accepting lower quality evidence for homeopathy (or any complementary medicine) than we do for conventional medicine? No way.

But knowing all of this, knowing that the most “potent” homeopathic remedies have precisely no active ingredient, that there is no evidence of benefit beyond placebo effect, that at best they’ll derive no therapeutic effect and at worse they may experience serious side effects, should an adult be allowed to choose homeopathy for themselves? Sure.  Do many users of homeopathy meet these basic criteria for informed consent? I very much doubt it.

Homeopathic Harms Vol 2: where’s the evidence?

We often harp on about the evidence for homeopathy working or otherwise, and I’m not going to touch on that here, because it’s been covered beautifully by many more eloquent writers than me.  What you don’t often see though, is comment on the evidence for homeopathy doing harm.  In the last post in this series the lovely @SParkleWildfire touched on medicalisation, an indirect harm that’s very real but tough to quantify; but what about direct harms?  I’m glad you asked…

In conventional medicine, randomised controlled trials are the best kind of study we can do of a drug to see if it works and if it it’s safe.  What maybe doesn’t mentioned quite so often is that there’s an even *better* form of evidence – the systematic review.  These are produced when someone sits down to do the very tough but remarkably important job of finding every single scrap of evidence they can on a given topic, and pooling it all together to try and get closer to the definitive answer.  The result is a document that represents the best evidence possible for how well a drug (or anything else, for that matter) works, and how safe it is.

One of the biggest and most respected sources of these systematic reviews is the Cochrane Collaboration, who cover all areas of medicine.  Happily, they also have a few reviews related to homeopathy, and that seems as good a place to start as any.  The most recently published is:

 Homeopathic Oscillococcinum® for preventing and treating influenza and influenza-like illness

The authors searched multiple databases of medical literature, covering a time period dating back to the mid-60s and all the way up until August 2012.  That’s a lot of literature.  Out of all the results they found six randomised, placebo-controlled trials of Oscillococcinum that were similar enough to be directly compared.  Since we’re not really interested in efficacy in this review, I’ll skip straight to the safety part: out of these six trials, including a total 1,523 people, there was one reported adverse event.  One. It happened to be a headache. Let’s stop and think about that for a moment.

A good quality randomised controlled trial collects every single adverse event that happens to every single patient.  And the use of the term “adverse event” is very deliberate, because it includes absolutely everything unexpected and unwelcome that happens (and here’s the key part) whether or not it’s likely to be related to taking the drug.  That might sound counter-intuitive, but the reason is simple – we want to pick up every possible side effect of drugs, and sometimes side effects are…weird.  So it might sound odd to include as an adverse event that someone got hit by a bus, but what if the drug they were taking made them dizzy, or confused, or clumsy?  It’s not unreasonable to suggest that any one of those things could end up in getting you involved in a traffic accident.  So every single little thing is recorded, and once the trials is over you do some sums to work out the key question – are these things *more likely to happen in the people who took the drug*? If 20 people broke a leg but they were equally spread out among the trial groups then nothing further needs to be said; if 19 of them were on the drug being studied then there might be something to worry about.  The flip side of that of course is that if 19 were in the placebo group, you might want to wonder if the drug is (perhaps unintentionally) promoting better balance and co-ordination, for example (or if everyone in the placebo group was a keen but inept snowboarder).

Is that one single adverse event out of over 1,500 people taking Oscillococcinum starting to look fishy yet?  What about if I drop in the snippet that some of the people involved (327, to be precise) took the remedy every day for four weeks, to see if it stopped them from getting flu in the first place?  How many times in four weeks would an average, healthy person experience something that you could call an adverse event – a headache, a tummy upset, indigestion, a strained ankle, a touch of insomnia?  I’ve had three of those things in the last 24 hours, and I wouldn’t say I’m a particularly remarkable individual.

So hopefully you can see from this that there’s simply a huge, yawning hole in the evidence about safety in homeopathy.  There are ways and means to address this (though they’re far from perfect), and I’ll address one of those in my next post in this series.

Plain language summary: calcium supplements and heart attacks

The research:

Calcium supplements with or without vitamin D and risk of cardiovascular events: reanalysis of the Women’s Health Initiative limited access dataset and meta-analysis

The summary:

This trial took information from 36,282 women who had been through the menopause, and looked at them to see whether taking calcium supplements made them more likely to have a heart attack.  Half of the women were given calcium and vitamin D supplements, while half were given a placebo (sugar-pill).  The trial found that taking calcium and vitamin D increased the risk of heart problems slightly, including heart attacks.  Some women took their own personal calcium supplements as well as those provided by the study, and these women had no increased risk of heart attack.

Re-analysis of some older trials found that calcium and vitamin D increased the risk of heart attacks and strokes.  The way that calcium supplements are used should be examined, to see if change is needed.

The caveats:

This paper appears to find that women who take the highest amount of calcium (their own tablets plus the ones provided by the study) have no increase in risk compared to women who don’t take any calcium at all.  If this was a true effect, we would expect women who take the most calcium to have the highest risk. Other authors have published papers that find no evidence of risk with calium and vitamin D supplements.

This paper is discussed in more detail in this blog post.