Posts filed under Medical news (265)

December 17, 2014

Good news, bad percentages

In the New York Times, a story reporting on new Ebola research, which suggests there are fewer unreported cases and less transmission in the general community than was previously thought. This is good news both because there aren’t as many cases, and also because control might be easier.

One unfortunate feature of the NYT story:

By looking at virus samples gathered in Sierra Leone and contract-tracing data from Liberia, the scientists working on the new study estimated that about 70 percent of cases in West Africa go unreported. That is far fewer than earlier estimates, which assumed that up to 250 percent did.

It’s hard to see how the scientific community could have assumed 250% of cases were unreported. Mark Lieberman at Language Log looks at the research paper to find, firstly, that the ‘70%’ and ‘250%’ are the unreported cases as a fraction of the reported cases. That is, 70% unreported means that for every 100 reported cases there are 70 unreported, which one would usually call 41% unreported.  He also notes that 70% is the upper bound of a range estimated the paper, with the best estimate being 17% (that is, 17/117, or 14.5% unreported). What seems to have happened is that the word ‘underreported’ was changed to ‘unreported.’

What Language Log doesn’t look at is the transmission of these percentages.  There’s a story (and press release)at Yale News, home of most of the researchers, which has an intermediate mutation

Researchers were also able to estimate that for every Ebola case reported, fewer than one went unreported. This estimate, that up to 70% of cases were not reported, is significantly lower than previous estimates. “For Sierra Leone, underreporting is lower than some more speculative estimates that ran as high as 250%,” Townsend noted.

with ‘underreporting’ in the direct quotation and ‘unreported’ in the main text. From there, it’s easy to see how the distinction could have been tidied away at the NYT and at TheHill.com

December 9, 2014

Health benefits and natural products

The Natural Health and Supplementary Products Bill is back from the Health Committee. From the Principles section of the Bill:

(c) that natural health and supplementary products should be accompanied by information that—

   (i)is accurate; and

   (ii)tells consumers about any risks, side-effects, or benefits of using the product:

(d)that health benefit claims made for natural health and supplementary products should be supported by scientific or traditional evidence.

There’s an unfortunate tension between (c)(i) and (d), especially since (for the purposes of the Bill) the bar for ‘traditional evidence’ is set very low: evidence of traditional use is enough.

Now, traditional use obviously does convey some evidence as to safety and effectiveness. If you wanted a herbal toothache remedy, you’d be better off looking in Ngā Tipu Whakaoranga and noting traditional Māori use of kawakawa, rather than deciding to chew ongaonga.

For some traditional herbal medicines there is even good scientific evidence of a health benefit. Foxglove, opium poppy, pyrethrum, and willowbark are all traditional herbal products that really are effective. Extracts from two of them are on the WHO essential medicines list, as are synthetic adaptions of the other two. On the other hand, these are the rare exceptions — these are the  ones where a vendor wouldn’t have to rely only on traditional evidence.

It’s hard to say how much belief in a herbal medicine is warranted by traditional use, and different people would have different views. It would have been much better to allow the fact of traditional use to be advertised itself, rather than allowing it to substitute for evidence of benefit.  Some people will find “traditional Māori use” a good reason to buy a product, others might be more persuaded by “based on Ayurvedic principles”.  We can leave that evaluation up to the consumer, and reserve claims of ‘health benefit’ for when we really have evidence of health benefit.

This isn’t treating science as privileged, but it is treating science as distinguished. There are some questions you really can answer by empirical study and repeatable experiment (as the Bill puts it), and one of them is whether a specific treatment does or does not have (on average) a specific health benefit in a specific group of people.

 

December 4, 2014

Fortune cookie science reporting

fortune_cookies

For science, the appropriate addition is “in mice.”

The Herald’s story (from the Daily Telegraph) “The latest 12 hour diet backed by science” has exactly this problem. It begins

Dieters hoping to shed the kilos should watch the clock as much as their calorie intake after scientists discovered that limiting the time span in which food is consumed can stop weight gain.

Confining meals to a 12-hour period, such as 8am to 8pm, and fasting for the remainder of the day, appears to make a huge difference to whether fat is stored, or burned up by the body.

It’s not until paragraph 6 that we find out this isn’t about dieters, it’s about mice.  The differences truly are huge — 5% of body weight within a few days, 25% by the end of the study — so you’d think it would be easy to demonstrate these benefits in humans if they were real.

Earlier this year, a different research group published a summary of studies on time-restricted feeding.  There are no controlled studies in humans. The uncontrolled studies aren’t especially high quality, and the ones with a 12-hour period mostly just take advantage of the no-daytime-eating rule observed by Muslims during the month of Ramadan. However, it’s still notable that the average weight reductions from a 4-week period of 12-hour food restrictions were 1-3%.

 

November 18, 2014

Cholesterol is bad for you

That doesn’t sound like a very interesting headline, but an important clinical trial whose results were released today has made definite steps towards re-convincing researchers on this point.

The trial, IMPROVE-IT, looked at adding a new drug, ezetimibe, to one of the standard statin drugs for cholesterol lowering, in people who had previously had a heart attack. Ezetimibe works by blocking cholesterol absorption in the gut, a completely different mechanism to the statins, which block cholesterol synthesis. The drug had previously shown unconvincing results in a preliminary study, made even less convincing by the behaviour of the manufacturer. There was increasing uncertainty that the cholesterol-lowering effect of the statins was really how they prevented heart disease, since no other drug appeared to be able to do the same thing.

Now, IMPROVE-IT has found a reduction in heart attacks and strokes. It’s very small — only 2 percentage points, even in this high-risk group of patients — but it looks real. Given the price of ezetimibe it probably won’t be widely used immediately, but it comes off patent in a few years and then use might spread a bit.  The results are also encouraging for dietary approaches to lowering cholesterol by reducing absorption: some cereals, and spreads with plant sterols.

Other stories: Forbes, New York Times 

November 12, 2014

Africa? Can you be more precise?

From the Telegraph (via many people on Twitter)

ebola

 

Seeing this at the same time as hearing about Bob Geldof’s Band-Aid reboot really emphasises the point that Africa isn’t a single place. The first Band-Aid recording was intended to help people in Ethiopia; the new one is for the Ebola-stricken regions of West Africa. The distance from Freetown to Addis Ababa is about the same as Auckland to Dili in East Timor, or Los Angeles to Bogota (or Addis Ababa to Prague).

On the other hand, the graph does make an important point. Syphilis, starvation, and TB are all very inexpensively treatable. Malaria and HIV are largely preventable, also at low cost. An effective treatment for Ebola will help, especially for medical personnel who are otherwise at very high risk, but in the long run it isn’t going to be enough. If we can’t deliver penicillin effectively, we won’t be able to deliver Ebola drugs. To make a real difference, we need a vaccine that’s good enough to prevent outbreaks.

November 7, 2014

What overdiagnosis looks like

An article in the New England Journal of Medicine talks about screening for thyroid cancer in South Korea. There has been a massive increase in diagnosis, mostly of very small tumours that are probably harmless — there was been no change in the thyroid cancer deaths.

thyroid

As the authors say:

Thyroid-cancer surgery has substantial consequences for patients. Most must receive lifelong thyroid-replacement therapy, and a few have complications from the procedure. An analysis of insurance claims for more than 15,000 Koreans who underwent surgery showed that 11% had hypoparathyroidism and 2% had vocal-cord paralysis.

 

October 30, 2014

Cocoa puff

Both Stuff and the Herald have stories about the recent cocoa flavanols research (the Herald got theirs from the Independent).

Stuff’s story starts out

Remember to eat chocolate because it might just save your memory. This is the message of a new study, by Columbia University Medical Centre.

 

Sixteen paragraphs later, though, it turns out this isn’t the message

“The supplement used in this study was specially formulated from cocoa beans, so people shouldn’t take this as a sign to stock up on chocolate bars,” said Dr Simon Ridley, Head of Research at Alzheimer’s Research UK.

 

There’s a lot of variation in flavanol concentrations even in dark chocolate, but 900mg of flavanols would be somewhere between 150g and 1kg of dark chocolate per day.  Ordinary cocoa powder is also not going to provide 900mg at any reasonable consumption level.

The Herald story is much less over the top. They also quote in more detail the cautious expert comments and give less space to the positive ones. For example, that the study was very small and very short, and the improvement in memory was just in one measure of speed of very-short-term recall from a visual prompt, or that this measure was chosen because they expected it to be affected by cocoa rather than because of its relevance to everyday life. There was another memory test in the study, arguably a more relevant one, which was not expected to improve and didn’t.

Neither story mentions that the randomised trial also evaluated an exercise program that the researchers expected to be effective but wasn’t. Taking that into account, the statistical evidence for the effect of flavanols is not all that strong.

October 28, 2014

Absolute, relative, correlation, cause

The conclusions of a recent research paper

Delivery by [caesarean section] is associated with a modest increased odds of [autism], and possibly ADHD, when compared to vaginal delivery. Although the effect may be due to residual confounding, the current and accelerating rate of[caesarean section] implies that even a small increase in the odds of disorders, such as [autism] or ADHD, may have a large impact on the society as a whole. This warrants further investigation.

The Herald

Babies born through Caesarean section are more likely to develop autism, a new study says.

Academics warn the increasingly popular C-section deliveries heighten the risk of the disorder by 23 per cent.

There’s a fairly clear difference in language: the news story is fairly clearly implying that caesarean sections cause autism; the research paper is being scrupulously careful not to say that.

Using a relative risk is convenient in technical communication, but in non-technical communication makes the impact seem greater than it really is. The US Centers for Disease Control estimate a risk of 1 in 68 for autism spectrum disorder (there aren’t systematic NZ data).  If the correlation with C-section really is causal, we’re talking about roughly 14 kids with autism spectrum disorders per 1000 without a C-section and about 17 per 1000 with a C-section. The absolute risk increase, if it’s real, is about 3 cases per 1000 C-sections.

It’s also important to be clear that this correlation cannot explain much of the recent increases in autism. A relative risk of 1.23 means that if we went from no C-sections to 100% C-sections there would be a 23% increase in autism spectrum disorder. The observed increase is about five times that, and since  C-sections have only increased about 10 percentage points, not 100 percentage points, the observed increase in autism is about 50 times what this correlation could explain.

There are (I’m told by people who know the issues) good reasons to think there are too many C-sections.  This probably won’t be one of the most important ones.

 

October 22, 2014

Screening the elderly

I’ve seen two proposals recently for population screening of older people. They’re probably both not good ideas, but for different reasons.

We had a Stat of the Week nomination for a proposal to screen people over 65 for depression at ordinary GP visits, to prevent suicide. The proposal was based on the fact that 70% of the suicides were in people who had visited a GP within the past month.  If the average person over 65 visits a GP less than about 8.5 times a year, this means those visiting their GP are at higher risk.  However, the risk is still very small: 225 over 5.5 years is 41/year, 70% of that is 29/year.

To identify those 29, it would be necessary to administer the screening question to a lot of people, at least hundreds of thousands. That in itself is costly; more importantly, since the questionnaire will not be perfectly accurate there will be  tens of thousands of positive results. For example, a US randomised trial of depression screening in people over 60 recruited 600 participants from 9000 people screened. In the ‘usual care’ half of the trial there were 3 completed suicides over the next two years; in those receiving more intensive and focused help with depression there were 2. The trial suggests that screening and intensive intervention does help with symptoms of major depression (probably at substantial cost), but it’s not likely to be a feasible intervention to prevent suicide.

 

The other proposal is from the UK, where GPs will be financially rewarded for dementia diagnoses. In contrast to depression, dementia is pretty much untreatable. There’s nothing that modifies the course of the disease, and even the symptomatic treatments are of very marginal benefit.

The rationale for the proposal is that early diagnosis gives patients and their families more time to think about options and strategies. That could be of some benefit, at least in the subset of people with dementia who are able and willing to talk about it, but similar advance planning could be done — and perhaps better — without waiting for a diagnosis.

Diagnosis isn’t like treatment. As a British GP and blogger, Martin Brunet, points out

We are used to being paid for things of course, like asthma reviews and statin prescribing, and we are well aware of the problems this causes – but at least patients can opt out if they don’t like it.

They can refuse to attend a review, decline our offer of a statin or politely take the pill packet and store it unopened in the kitchen cupboard. They cannot opt out of a diagnosis.

 

October 9, 2014

…and to divide the light from the darkness

Q: There’s a story that charging your phone in your bedroom make you fat.

A: Yes, there is.

Q: Why?

A: Because it looked like a good headline.

Q: No, why does it make you fat?

A: Melatonin. The theory is that any light at night time makes your body not produce enough melatonin and that this is bad.

Q: How much more did people who charged their phones in their bedroom end up weighing?

A: There weren’t any people involved.

Q: Ok, so they had mice with cellphones in their bedrooms?

A: Rats. And not cellphones.

Q: Some other light source of a similar brightness?

A: No.

Q: What, then?

A: They put melatonin in the rats’ drinking water.

Q: So that should make them lose weight. Did it?

A: Not that they reported.

Q: Can you work with me here?

A: They measured the conversion of fat under the rats’ skin from ‘white’ to ‘brown‘, which is theoretically relevant to energy use and perhaps to diabetes and heart disease. It’s interesting research. (abstract)

Q: So it could be relevant, but doesn’t the generalisation seems a bit indirect?

A: Yes, “a bit.”

Q: Do international patterns of cellphone use match patterns of obesity?

A: Not really, but maybe in East Asia they use different chargers or something.

Q: Is the LED on a charger really enough to make a difference?

A: That’s what the story lead implies, but the second paragraph talks about research involving phone screens, laptops, artificial lighting, and street lights, so I’m guessing there’s a bit of a bait and switch going on.

Q: Couldn’t it be enough? I mean, in nature, it would be completely dark at night, like they say.

A: Only up to a point. There was another relevant story today, too.