Posts filed under Medical news (341)

The Herald reports on a nice comparison of Accident Compensation Commission claims rates for cycling and other activities. Michael Chieng, an Auckland medical student, found that the risk of a ACC claim was 35 times higher per rugby game than per two hour cycle ride, with cycling also safer than skiing and horseriding.  The health benefits of cycling are almost certainly greater than the risks, which is why helmet laws aren’t very good public health interventions.

It’s still a bit unfortunate that cycling was compared only to recreational activities, not to other ways of getting from point A to point B. I’m pretty sure that it’s less safe than walking or riding a bus. Also, unlike rugby and skiing, cycling in New Zealand is a lot more dangerous than it should be.

Sadly, I do have to point out, yet again, that there is not only no link to the research, there doesn’t even seem to be a source to link to.

The Herald (from the Daily Mail again, sigh) has a story about deadly mouthwash

Using mouthwash is a ‘disaster’ for health, increasing the risk of heart attacks and strokes, scientists are warning

In a small experimental study, 19 people who spent two weeks using a type of mouthwash not recommended for long-term use ended up with slightly higher blood pressure, by 2-3.5mmHg (or ‘mmgh’ as the story says). This was an uncontrolled study and everyone had the with-mouthwash and without-mouthwash experimental periods in the same order, so it could just have been a problem of experimental design, but it’s quite plausible that it’s true, and similar results have been found in the past.

What’s a bit surprising is that the story regards this as entirely a bad thing. The hypothesised reasons for the blood pressure difference is that the mouthwash kills bacteria in the mouth that make nitrite. You probably have heard of nitrite in previous Herald or Daily Mail stories.  It’s usually  described as a preservative for cured meats and is anathematised for its presumed potential to cause cancer. Even the introduction in the mouthwash research paper mentions that nitrite has traditionally been regarded as harmful and doesn’t give any of the recent evidence to the contrary.

There is also a widespread belief, though based on relatively weak evidence, that gum and mouth infections increase the risk of heart disease. Since the type of mouthwash being studied is recommended only for treatment, not for long-term use, it might easily decrease rather than increase the risk of heart disease if used as recommended.

It’s not obvious whether the benefits of mouthwash for chronic disease would outweigh the disadvantages, even if the research had studied the sorts of mouthwash (such as Listerine) intended for daily use. It is clear that the context, even context present in the abstract of the open-access research paper, is being ignored.

From the Herald: “Herbs, berries and red wine could create diabetes barrier”

High intakes of the flavonoids are linked to lower insulin resistance and better control of blood sugar, a study has shown.

Both effects help stave off the onset of Type 2 diabetes

That’s better than the Daily Mail lead

It sounds like the ingredient list for an indulgent dessert. But red wine, chocolate and strawberries are more than a guilty pleasure. They could all help guard against diabetes.

But it’s still misleading.  The study (newspapers,would it kill you to link?) didn’t measure diabetes in anyone, just an estimate of insulin resistance.

More importantly, the difference is tiny. No, smaller than that. The difference in the insulin resistance estimate between the 20% of participants with the highest and lowest flavanoids in the diet was 0.1. The standard deviation of insulin resistance was 1.6. For people who aren’t as used to visualising this sort of difference, this is what it would look like if they were Normal distributions

As usual, the StatsChat advice is that there are good reasons to consume red wine and chocolate, but preventing diabetes is not one of them.

The Council on Foreign Relations has built an interactive map showing outbreaks of the major vaccine-preventable diseases since mid-2008, based on news stories. Here’s the local map

The red circles are measles; the green are pertussis; blue are rubella.

There are two big limitations to the use of news stories as the source. The first is obvious from the map. That outbreak of 3500 pertussis cases in Western Australia wasn’t actually among the Ngaanyatjarra people of the Western Desert, where the circle is. It was mostly in Perth, but the story didn’t say that, just “Western Australia”.

The second limitation is that not everything gets reported. Here’s a map of more of the world

The small orange circles are  polio, and probably include every polio case diagnosed in the world. The larger, yellow circles include cholera and typhoid, and are just big outbreaks. The brown circles are mumps, which only seems to make the news in Europe and the Middle East. And there’s basically no pertussis reported in Africa or South Asia, because it’s underdiagnosed and not really news.

An NPR News story on back pain and its treatment

One reason invasive treatments for back pain have been rising in recent years, Deyo says, is the ready availability of MRI scans. These detailed, color-coded pictures that can show a cross-section of the spine are a technological tour de force. But they can be dangerously misleading.

This MRI shows a mildly herniated disc. That’s the sort of thing that looks abnormal on a scan but may not be causing pain and isn’t helped by surgery.

“Seeing is believing,” Deyo says. “And gosh! We can actually see degenerated discs, we can see bulging discs. We can see all kinds of things that are alarming.”

That is, they look alarming. But they’re most likely not the cause of the pain.

If some event is rare, then your survey sample won’t have many people who truly experienced it, so even a small rate of error or false reporting will overwhelm the true events, and can lead to estimates that are off by a lot more than the theoretical margin of sampling error.

The Herald has picked up on one of the other papers (open access, not linked) in this year’s Christmas BMJ, which looks at data from the National Longitudinal Study of Youth, in the US. This is an important social and health survey, and the paper is written completely seriously. Except for the topic

Of 7870 eligible women, 5340 reported a pregnancy, of whom 45 (0.8% of pregnant women) reported a virgin pregnancy (table 1). Perceived importance of religion was associated with virginity but not with virgin pregnancy. The prevalence of abstinence pledges was 15.5%. The virgins who reported pregnancies were more likely to have pledged chastity (30.5%) than the non-virgins who reported pregnancies (15.0%, P=0.01) or the other virgins (21.2%, P=0.007).

and

A third group of women (n=244) not included in analysis, “born again virgins,” reported a history of sexual intercourse early in the study but later provided a conflicting report indicating virginity. Reports of pregnancy among born again virgins were associated with greater knowledge of contraception methods with higher failure rates (withdrawal and rhythm methods) and lower interview quality (data not shown), and reports from this group may be subject to greater misclassification error.

The survey had carefully-designed and tested questions, and used computer-assisted interviewing to make participants more willing to answer potentially embarrassing questions. It’s about as good as you can get. But it’s not perfect.

You may remember StatsChat’s criticism of data quality and analysis in paper about chocolate and Nobel Prizes from a leading medical journal.  Another leading medical journal, BMJ, traditionally has a Christmas issue with not entirely serious papers, typically based on good-quality silly research. One of the past highlights was the systematic review of randomised trials of parachute use.

This year, there’s a survival analysis of chocolate in hospital wards. Survival analysis is the branch of statistics working with the time until an event happens.  Often the event is death, hence the name ‘survival’, but it could be something else bad, such as a heart attack, or something good, such as finding a job.  If you’re a chocolate, it’s being eaten.

The data are a good fit to a constant hazard of consumption, with a rate of just under 1%/minute.  There isn’t any sign of strong heterogeneity — if some chocolates are preferred to others, the preference is either not strong enough or variable enough between people that no chocolates are safe.

Other papers in the Christmas issue include a semi-serious comparison of stem cell size and structure for mice and whales, and the finding that, in Dublin, people called Brady are more likely to have pacemaker treatment for bradycardia (presumably a multiple comparison issue)

From TV One Breakfast this morning “WiFi detrimental to health, study suggests“. (I didn’t see this live; the Science Media Centre contacted me for comment)

The guest, Mr Kasper from Safe Wireless Technology NZ, said

Overseas research has shown that a person who uses a mobile phone for a year increases their chances of getting brain cancer by 70%, according to the SWTNZ.

The ‘overseas research’ appears to be this, a case-control study of acoustic neuroma in Scandinavia. The first thing to note is that “acoustic neuroma” isn’t the same thing as “brain cancer”. Acoustic neuroma is a rare, benign brain tumour (‘benign’ means it doesn’t spread metastatically), which is usually treatable, though often with long-term effects.  The researchers didn’t suggest that their results applied to other brain tumours; in fact, they assumed the opposite and used people with a different brain tumour, meningioma, as one set of controls for their comparisons.

The story  also says

“There’s so much research and there’s so much scientific evidence now that does more than just suggest that there is a real problem, and people are getting these problems,” Mr Kasper said.

The National Cancer Institute has a good summary of the scientific evidence, and they are not at all convinced. It certainly isn’t the case that there’s a strong association with brain cancer overall.

The new research appears to be better conducted than a lot of the past claims of associations between radio waves and health. It’s working against a strong burden of proof both from animal studies and from the fact that radio waves can’t damage DNA. I don’t think it manages that level of proof, but I think reasonable people could disagree. However, even if we assume that the association specifically with acoustic neuroma is real and causal, it doesn’t really support any concern over WiFi. Cellphones are pressed up against the ear, and so provide higher dose of radio-frequency energy to that ear. WiFi transmitters are typically not pressed up against the ear, and each doubling of the distance reduces the energy by a factor of four. And, since they don’t have to reach as far, WiFi signals are less powerful to begin with.

The story ends with

“We do want the Government to put some money into some independent research.”

I’m generally in favour of the Government putting money into research, but on this particular topic  there’s no real advantage to the research being done in New Zealand, and we have too small a population to contribute much. There are large international studies ongoing; we don’t need a small local one.

If you are worried about cellphones and acoustic neuroma, use headphones with your cellphone. If you are worried about WiFi and brain cancer, then relax.

I’ve written before about the Seralini research that involved feeding glyphosate and GM corn to rats. Now, Retraction Watch is reporting that the paper will be retracted.

This is a slightly unusual retraction: typically either the scientist has a horrible realisation that something went wrong (maybe their filters were affecting composition of their media) or the journal has a horrible realisation that something went wrong (maybe the images were Photoshopped or the patients didn’t actually exist).

The Seralini paper, though, is being retracted for being kinda pointless. The editors emphasise that they are not suggesting fraud, and write

A more in-depth look at the raw data revealed that no definitive conclusions can be reached with this small sample size regarding the role of either NK603 or glyphosate in regards to overall mortality or tumor incidence. Given the known high incidence of tumors in the Sprague-Dawley rat, normal variability cannot be excluded as the cause of the higher mortality and incidence observed in the treated groups.

Ultimately, the results presented (while not incorrect) are inconclusive, and therefore do not reach the threshold of publication for Food and Chemical Toxicology. 

They’re certainly right about that, but this is hardly a new finding. I’m not really happy about retraction of papers when it isn’t based on new information that wasn’t easily available at the time of review. Too many pointless and likely wrong papers are published, but this one is being retracted for being pointless, likely wrong, and controversial.

[Update: mass enthusiasm for the retraction is summarised by Peter Griffin]

The Daily Mail strikes again, in today’s Herald story headlined “Gene explains why girls like sweet stuff more than boys”

The actual research did an experiment to look at differences in what snacks children chose. The difference they found was in fat consumption, not sugar, and, overall, girls actually ate a bit less than boys, not more. Here’s the graph from the paper

The potentially interesting finding was that the difference between kids with two versions of the gene was larger for girls than boys, suggesting that the gene may act differently in boys and girls.