Posts filed under Medical news (341)

Says the Herald (reprinting the Daily Mail)

If you have always found doing sums a struggle, you might just be able to blame your mother.

Because research has linked a woman’s hormone levels in pregnancy with her child’s maths skills at age five.

Boys and girls whose mothers were very low in the hormone thyroxine were almost twice as likely to do badly in arithmetic tests, it found.

The hormone in question is thyroxine, produced by the thyroid, and the basic issue is that iodine deficiency is getting more common again. In Australia and New Zealand, iodine has been added to bread since September 2009 to address this problem. In Australia, the fortification of bread has been fairly successful; there doesn’t seem to be data for New Zealand, but there’s no reason to expect it to be different. So the story  may not be applicable to New Zealanders.

Also, as with the cannabis paper a couple of weeks ago, the “twice as likely” is simply wrong.  Doing badly in arithmetic was defined as being in the bottom 50%, and it’s not plausible that low-thyroxine kids are twice as likely to be in the bottom half.  In fact, it’s the odds ratio for being in the lower 50% of students in maths that was 1.79.  Since the overall odds of being in the bottom half is 1:1, if you multiply by 1.79 you get 1.79:1, which is a probability of 64% of being in the bottom half.

A difference between 50% and 64% is not “almost twice as likely”, and “blame” is a completely inappropriate term — this is new research, so even if it’s true (it could be) and relevant to New Zealand (it probably isn’t) it would not be something for which ‘blame’ would be appropriate. There’s entirely too much blaming mothers already.

From the Herald

Men who are bald at age 45 are more likely to develop aggressive prostate cancer compared with those who keep their hair.

US researchers found those who lose hair at the front of their heads and have moderate hair-thinning on the crown were 40 per cent more likely to develop a fast-growing tumour in their prostate.

This was compared with men with no baldness.

That’s all true, but what casts doubt on this finding is that you get the same results if you compare to men with severe baldness. That is, the research found a higher rate of aggressive prostate cancer in men who had ‘moderate’ baldness on the top of head, but not in those who had milder or more severe forms, and no increase in non-aggressive prostate cancer. Here are the estimated relative increases in risk, with confidence intervals

When you consider the lack of a consistent trend, and the fact that the evidence isn’t all that strong for the moderate-baldness/aggressive-cancer combination, I don’t think this is worth getting all that excited about.

This one can mostly be blamed on the journal: the American Society of Clinical Oncology press release isn’t too bad in itself, but if you compare it to the other recent occasions when ASCO have issued a press release, it doesn’t really measure up.

3News

Teenagers who use cannabis daily are seven times more likely to attempt suicide and 60 percent less likely to complete high school than those who don’t, latest research shows.

Me (via Science Media Center)

“The associations in the paper are summarised by estimated odds ratios comparing non-users to those who used cannabis daily. This can easily be misleading to non-specialists in two ways. Firstly, nearly all the statistical evidence comes from the roughly 1000 participants who used cannabis less than daily, not the roughly 50 daily users — the estimates for daily users are an extrapolation.

“Secondly, odds ratios are hard to interpret.  For example, the odds ratio of 0.37 for high-school graduation could easily be misinterpreted as a 0.37 times lower rate of graduation in very heavy cannabis users. In fact, if the overall graduation rate matched the New Zealand rate of 75%, the rate in very heavy cannabis users would be 53%, and the rate in those who used cannabis more than monthly but less than weekly would be 65%.

That is, the estimated rate of completing high school is not 60% lower, it’s about 20% lower.  This is before you worry  about the extrapolation from moderate to heavy users and the causality question. The 60% figure is unambiguously wrong. It isn’t even what the paper claims.  It’s an easy mistake to make, though the researchers should have done more to prevent it, and that’s why it was part of my comments last week.

You can read all the Science Media Centre commentary here.

[Update: The erroneous ‘60% less likely to complete high school’ statement is in the journal press release. That’s unprofessional at best.]

(I could also be picky and point out 3News have the journal wrong: The Lancet Psychiatry, which started this year, is not the same as The Lancet, founded in 1823)

You have probably seen the graphic from vox.com

There are several things wrong with it. From a graphics point of view it doesn’t make any of the relevant comparisons easy. The diameter of the circle is proportional to the deaths or money, exaggerating the differences. And the donation data are basically wrong — the original story tries to make it clear that these are particular events, not all donations for a disease, but it’s the graph that is quoted.

For example, the graph lists $54 million for heart disease, based on the ‘Jump Rope for Heart’ fundraiser. According to Forbes magazine’s list of top charities, the American Heart Association actually received $511 million in private donations in the year to June 2012, almost ten times as much.  Almost as much again came in grants for heart disease research from the National Institutes of Health.

There’s another graph I’ve seen on Twitter, which shows what could have been done to make the comparisons clearer:

It’s limited, because it only shows government funding, not private charity, but it shows the relationship between funding and the aggregate loss of health and life for a wide range of diseases.

There are a few outliers, and some of them are for interesting reasons. Tuberculosis is not currently a major health problem in the US, but it is in other countries, and there’s a real risk that it could spread to the US.  AIDS is highly funded partly because of successful lobbying, partly because it — like TB — is a foreign-aid issue, and partly because it has been scientifically rewarding and interesting. COPD and lung cancer are going to become much less common in the future, as the victims of the century-long smoking epidemic die off.

Depression and injuries, though?

Update: here’s how distorted the areas are: the purple number is about 4.2 times the blue number

Two examples of neighbourly correlations, at least one of which is not causation

1. A (good) Herald story today, about research in Michigan that found people who got on well with their neighbours were less likely to have heart attacks

2. An old Ministry of Justice report showing people who told their neighbours whenever they went away were much less likely to get burgled.

The burglary story is the one we know is mostly not causal.  People who tell their neighbours whenever they go on holiday were about half as likely to have experienced a burglary, but only about one burglary in seven happened while the residents were on holiday. There must be something else about types of neighbourhoods or relationships with neighbours that explains most of the correlation.

I’m pretty confident the heart-disease story works the same way.  The researchers had some possible explanations

The mechanism behind the association was not known, but the team said neighbourly cohesion could encourage physical activities such as walking, which counter artery clogging and disease.

That could be true, but is it really more likely that talking to your neighbours makes you walk around the neighbourhood or work in the garden, or that walking around the neighbourhood and working in the garden leads to talking to your neighbours? On top of that, the correlation with neighbourly cohesion was rather stronger then the correlation previously observed with walking.

You know how you read a fortune and add “…in bed” to the end of it? Feel like I should add “…in mice” to most big science headlines.

— Jordan Gaines Lewis (@GainesOnBrains) July 11, 2014

Or, often in NZ papers, “… in the UK”.

There’s a Herald story with the lead

More than 12,000 new cases of cancer every year can be attributed to the patient being overweight or obese, the biggest ever study of the links between body mass index and cancer has revealed.

Since there about about 20,000 new cases of cancer a year in NZ, that would be quite a lot.  The story never actually comes out and says the 12,000 is for the UK, but it is, and if you read the whole thing it becomes fairly clear.  It still seems the sort of context that a reader might find helpful.

Australia and New Zealand are introducing new food labelling legislation that will reduce the scope for bogus health and nutrition claims (the only bogus claims allowed will be the ones that slipped into the official code).  This is a Good Thing, as I have said in the past.

The legislation also says you can’t make health claims about booze. This is probably a Good Thing, although I don’t see why calorie/carbohydrate claims shouldn’t be allowed.  However, there’s a serious bug in the standards: one of the claims that’s specifically disallowed for alcoholic beverages is “gluten-free.”

It’s true that “gluten-free” has become a trendy bogus nutrition claim, but it’s also vital health information for some people, particularly those with coeliac disease. In that context, “gluten-free” is more like an allergen warning (“May contain nuts”) than a nutrition warning.  In fact, if you look at the section on “Mandatory Warning and Advisory Statements and Declarations”, Clause 4 includes

Cereals containing gluten and their products, namely, wheat, rye, barley, oats and spelt and their hybridised strains other than where these substances are present in beer and spirits standardised in Standards 2.7.2 and 2.7.5 respectively

along with peanuts, soybeans, eggs, milk, etc.  That is, declaring the presence of gluten is mandatory except in beer, where it is the only one of the Clause 4 mandatory warnings that becomes forbidden.  Banning gluten-free labelling on beer is deliberate and planned, it didn’t just fall between the cracks.

Since this is a trans-Tasman law, it’s going to be a pain to revise.  There seems to be one possible loophole. In the Nutrition/Health claims standards, there is provision for endorsements by independent endorsing bodies. These are exempted from most of the health/nutrition regulations: as the Explanatory Text says:

Endorsements are exempt from the other requirements of the Standard (except clause 7), to allow for endorsement programs which use the criteria set by the endorsing body.

It appears (though I may have missed something, and I’m not a lawyer) that Coeliac New Zealand could still endorse gluten-free beers, even though the brewers couldn’t make the same claims themselves.

[Further update: MPI contacted Keruru Brewery and say they are now working on a solution for gluten-free beer.]

[update: I heard about this on Twitter, but the blog post that kicked off Twitter is here]

I’ve mentioned a number of times that statistics on cancer survival are often unreliable for the conclusion people want to draw, and that you need to look at cancer mortality.  Today’s story in Stuff is about Otago research that does it right:

The report found for 11-year timeframe, cancer-specific death rates decreased in both countries and cancer mortality fell in both countries. But there was no change in the difference between the death rates New Zealand and Australia, which remained remained 10 per cent higher in New Zealand.

That is, they didn’t look at survival after diagnosis, they looked at the rate of deaths. They also looked at the rate of cancer diagnoses

“The higher mortality from all cancers combined cannot be attributed to higher incidence rates, and this suggests that overall patient survival is lower in New Zealand,” Skegg said.

That’s not quite as solid a conclusion — it’s conceivable that New Zealand really has higher incidence, but Australia compensates by over-diagnosing tumours that wouldn’t ever cause a problem — but it would be a stretch to have that happen over all types of cancer combined, as they observed.

Stuff has a story from the LA Times about exercise and breast cancer risk.  There’s a new research paper based on a large French population study, where women who ended up having a breast cancer diagnosis were less likely to have exercised regularly for the past five year period.  This is just observational correlation, and although it’s a big study, with 2000 breast cancer cases in over 50000 women, the evidence is not all that strong (the uncertainty range around the 10% risk reduction given in the paper goes from an 18% reduction down to a 1% reduction).  Given that,  I’m a bit unhappy with the strength of the language in the story:

For women past childbearing age, a new study finds that a modest amount of exercise — four hours a week of walking or more intensive physical activity such as cycling for just two hours a week — drives down breast cancer risk by roughly 10 per cent.

There’s a more dramatically wrong numerical issue towards the end of the story, though:

The medications tamoxifen and raloxifene can also drive down the risk of breast cancer in those at higher than average risk. They come with side effects such as an increased risk of deep-vein thrombosis or pulmonary embolism, and their powers of risk reduction are actually pretty modest: If 1000 women took either tamoxifen or raloxifene for five years, eight breast cancers would be prevented.

By comparison, regular physical activity is powerful.

Using relative risk reduction for the (potential) benefits of exercise and absolute risk reduction for the benefits of the drugs is misleading. Using the breast cancer risk assessment tool from the National Cancer Institute, the five-year breast cancer risk for a typical 60 year old is perhaps 2%. That agrees with the study’s 2000 cases in 52000 women followed for at least nine years.  If 1000 women with that level of risk took up regular exercise for five years, and if the benefits were real,  two breast cancers would be prevented.

Exercise is much less powerful than the drugs, but it’s cheap, doesn’t require a doctor’s prescription, and the side-effects on other diseases are beneficial, not harmful.

A nice story in the Herald about a randomised trial of hand sanitiser dispensers in schools.

The study, published today in the journal PLoS Medicine, found absence rates at schools that installed dispensers in classrooms as part of the survey were similar at those “control” schools which did not.

There’s even a good description of the right way to do sample size calculations for a clinical trial

Beforehand, the authors believed a 20 per cent reduction in absences due to illness would be important enough to merit schools considering making hand sanitiser available, so designed the study to detect such a difference.

“Some previous studies suggested that there could be a bigger effect than that, but we wanted to be sure of detecting an effect of that size if it was there,” Dr Priest told the Herald.

That is, the study not only failed to find a benefit, it ruled out any worthwhile benefit. Either Kiwi kids are already washing their hands enough, or they didn’t use the supplied sanitiser.

My only quibble is that the story didn’t link to the open-access research paper.