CHAPTER 10 - All your ills come from thoughts

I’m not sure who first said it, but there’s a lot of truth in the axiom, “If it sounds too good to be true, then it probably is.”

I think the same also applies to the bad.  If it sounds too bad to be true, then it probably is.  Sometimes there are things said that sound so extreme that we wonder whether they’re plausible.

When I first read Dr Leaf’s statement, “A massive body of research collectively shows that up to 80% of physical, emotional and mental health issues today could be a direct result of our thought lives” [1: p15], I wondered whether it could be plausible.  80% is a pretty big number, and as a GP with a fairly broad experience behind me, that number didn’t match what I have seen in my office every day for the last ten years.

Unfortunately, none of her references listed any quotes or information citing thought as causing 80% of all illness.  Indeed, her endnote pointed to a collection of a few peer reviewed articles and official websites.  The rest were university links without any data at all, a few books, and a documentary talking about epigenetics.  Therefore, her statement that “a massive body of research” documented the relationship of thought and disease is an exaggeration.

I wondered if she may have adapted her statement from a quote provided on one of her main source websites, from Dr Paul Rosch, M.D., President of the American Institute of Stress.  He said that "75 to 90% of all visits to primary care physicians result from stress-related disorders." [132]

That, too, was another hard number to swallow.  The BEACH study, an Australian study constantly tracking general practitioners and their patients, their demographics, diagnoses and subsequent services, suggests a total of about 8% of consultations were related to psychological issues [133].  Unless the US population is radically different to Australia, Dr Rosch’s assertion is still overblown by nearly a factor of ten.

So there really could only be two explanations – I’ve been missing huge swathes of thought related illnesses over the last ten years of my professional life, or reality is a lot different to what Dr Leaf suggests.

Thankfully when Dr Leaf revised her figures in her new book [2: p37-8], she also published her sources, so it’s possible to properly review exactly how she arrived at her conclusion, and compare it to the peer-reviewed, independent medical literature.

That’s what this chapter is all about.

I propose that Dr Leaf’s assertion that “75 to 98 percent of mental and physical illness comes from ones thought life” is incorrect, and indeed, implausible.  In the first part of the chapter, I review the validity of Dr Leaf’s statistics and their sources, their strengths and weaknesses, and the validity of how Dr Leaf interprets and applies them.  The second part of the chapter outlines evidence from the peer-reviewed literature, which will show that Dr Leaf’s assertion is contrary to modern medical science and common logic.

Dr Leafs “Sources”

On page 37 and 38 of her 2013 work, Dr Leaf lists seven bullet points which she cites as evidence that 75 to 98 percent of mental and physical illness come from our thought life [2].  Lets review and analyze them separately.

“A study by the American Medical Association found that stress is a factor in 75% of all illnesses and diseases that people suffer from today.”

First of all, the paper that Dr Leaf refers to, Cohen et al [232], was not by the American Medical Association, but by researchers from Carnegie Mellon University and University of British Columbia.  It was published in the Journal of the American Medical Association, an esteemed journal that has been publishing independent medical research for the last century or so.  It may seem trivial, but an active research scientist should know the difference between who did the study and who published the study.  Errors like this simply undermine Dr Leaf’s credibility.

The article itself provides a good discussion on why stress is associated with some diseases, cardiovascular disease in particular (which we established in the previous chapter.  No one’s denying that fact!)

But nowhere in that article does it say that stress is associated with 75% of illnesses today.  Nowhere.  I read it three times and used a search engine to make sure I wasn’t missing anything.  I’ll say it again - nowhere in the article was the figure of 75% even mentioned once.

Besides, the article provided no conclusive evidence that stress caused any of the four diseases they mentioned, only that there was an association.  Remember, correlation does not equal causation.  In fact, the authors discussed the significant weakness in ascribing stress to certain diseases, not just once, but several times. 

For example, “Although stressors are often associated with illness, the majority of individuals confronted with traumatic events and chronic serious problems remain disease-free.”

Yet Dr Leaf maintains that the majority of illness is related to stress.  Her own source directly contradicts her fundamental assertion.  Indeed, it appears that she didn’t actually quote the article, just misrepresented it.

“The association between stress and disease is a colossal 85%”

In his book, “Managing Stress: Principles and Strategies for Health and Well-Being”, Dr Seaward said, “Some health experts now speculate that perhaps as much as 70 to 85 percent of all diseases and illnesses are stress-related.” [233]

He also quotes the claim of the American Institute of Stress that “80% of all visits to primary care physicians are for stress-related complaints or disorders.”  I’ll discuss this one in more detail soon.

But notice the language he used: “SOME health experts now SPECULATE that PERHAPS AS MUCH as 70 to 85 percent of all diseases and illnesses are stress-related” (emphasis added).

The best Dr Seaward can do is to say that the figure of 70 to 85 percent is the very top of a very broad figure, a figure that’s a wild guess by the minority of health experts.  That doesn’t sound particularly credible.

“The International Agency for Research on Cancer and the World Health Organization have concluded that 80% of cancers are due to lifestyles and are not genetic, and they say this is a conservative number”

The International Agency for Research on Cancer and the World Health Organization are leaders in research and health policy formation, and the mention of those organizations in a quote would usually assure validity.  And I’m sure the IRC and the WHO probably did conclude that 80% of cancers were due to lifestyles and were not genetic … back in 1979.

Dr Leaf’s source for this citation is “Cancer statistics and views of causes” Science News Vol.115, No 2 (Jan.13 1979), p23. Referencing a journal on genetics from 1979 is the equivalent of attempting to use the “Car-of-the-Year” from 1979 to justify your current choice of vehicle.  The technology has advanced significantly, and genetic discoveries are light-years ahead of where they were more than three decades ago.  For example, Naidoo et al noted that, “the GWAS approach has dramatically changed the field of human disease genetics, from identifying mostly irreproducible disease associations in the pre-GWAS era to revealing thousands of statistically robust single nucleotide polymorphism (SNP) associations today.” [234]

On the link between stress and cancer, Cohen et al corrects Dr Leaf (again), “Despite these promising findings, evidence from prospective studies linking stress and cancer incidence in humans is mixed at best.” [232]

I’ll discuss this in more detail soon, but according to the most recent cancer statistics [206], prostate cancer is the most prevalent form of cancer.  However, there is no evidence that prostate cancer is influenced by any environmental factors [207, 208].

So it’s clear that Dr Leaf relies on an outdated historical reference to try and justify her current hypothesis, while up-to-date scientific findings are contradictory.

“According to Dr Bruce Lipton, a scientist who has made great strides in understanding the effect of our thinking on our brain, gene disorders like Huntington’s chorea, beta thalassemia and cystic fibrosis, to name a few, affect less than 2% of the population. This means the vast majority of the worlds population come into this world with genes that should enable them to live happy and healthy lives. Lipton says a staggering 98% of diseases are lifestyle choices - in other words, our thinking.”

Dr Bruce Lipton is a paradox.  According to his own book, he is a cell biologist who has published a number of peer-reviewed papers in the field, but suffered a stress-related meltdown, and then had a self-described epiphany about the nature of thought and biology.  He now teaches in a chiropractic college in New Zealand [235].  So he switched from studying and teaching reputable science to teaching pseudoscience [236-238]

He is a self-confessed mystic who believes that God is the Earth’s biosphere.  I quote, “A number of you critical readers may rightly be skeptical of my claim that Earth is Heaven.  For by definition, Heaven is also the abode of the Deity and the blessed dead … This Earth is Heaven?  The Deity lives here?  He knows the Deity?  The answers to those questions are: yes, yes, and I believe I do.  Well, to be completely honest, I don't know all of you.  For God's sake there are over six billion of YOU.  And to be fully honest, I don’t really know all of the members of the plant and animal kingdom either, though I believe that they also comprise God.  In the immortal words of Tool time's Tim Taylor: ‘Baaaaack the truck up!  Is he saying that humans are God?’  Well … yes, I am.” [235: page xxvi]

He published his last scientific paper in 1992 and started publishing non-mainstream work in 1998.  I did a search for his articles using Google Scholar and Pubmed, and since 1998, the only papers I could find that cite him are non-mainstream.

Let me clarify: Just because someone’s not recognised by the mainstream scientific community does not automatically disqualify their opinions.  But it does conflict with Dr Leafs description of him as “a scientist who has made great strides in understanding the effect of our thinking on our brain.”  That’s Dr Leaf’s interpretation, not one shared by the scientific community.

Even allowing for Dr Lipton’s alternative worldview and propensity for pseudoscience, a much greater problem for this citation is Dr Leaf’s hyperbolic paraphrasing.

What Dr Lipton said in his book was,
"Of course, there is no doubt that some diseases, like Huntington's chorea, beta thalassaemia, and cystic fibrosis, can be blamed entirely on one faulty gene.  But single gene disorders affect less than two percent of the population; the vast majority of people come into this world with genes that should enable them to live a happy and healthy life.  The diseases that are today's scourges - diabetes, heart disease, and cancer - short circuit a happy and healthy life.  These diseases, however, are not the result of a single gene, but of complex interactions among multiple genes and environmental factors." [235]

I agree with Lipton’s fundamental premise - most human traits are born of a complex interaction between multiple genes and the environment – though he goes beyond the best evidence of science by claiming the environment is the dominant force over genetic factors.  Later in his work, he goes well beyond the boundaries of scientific credibility by suggest there’s a metaphysical link between cell function and our beliefs.  Dr Leaf then exaggerates Lipton’s distortion by reinterpreting his words to suit her assumptions.

Dr Lipton’s statement:

“These diseases, however, are not the result of a single gene, but of complex interactions among multiple genes and environmental factors.”

has been morphed by Dr Leaf into:

“Lipton says a staggering 98% of diseases are lifestyle choices - in other words, our thinking.”

Note the difference - Lipton didn’t say anything about thinking or lifestyle choices.  That’s Dr Leaf’s interpretation.  Dr Lipton made it clear that the interplay is within “the environment”, not thought. Dr Leaf misinterprets, misquotes, and misleads.

“According to W.C Willett (balancing lifestyle and genomics research for disease prevention Science (296) p 695-698, 2002) only 5% of cancer and cardiovascular patients can attribute their disease to hereditary factors.” 

Unlike most of Dr Leaf’s sources, Professor Willett is the real deal.  He is a Professor of Epidemiology at the Harvard School of Public Health.  He is a lead authors of large, long-term cohort studies such as the Nurses Health Study.  His opinion is worthy of attention, which is why it’s such a shame when Dr Leaf erroneously quotes his research.

For example, in the paper that Dr Leaf cited, Prof Willett said, “Highly penetrant mutations, which account for conspicuous clustering of diseases within families, are rare and appear to account for less than 5% of major cancers and coronary heart disease.” [239]

The first thing to point out is that this paper dates back to 2002.  Even though it was only published twelve years ago, genetic research has improved exponentially since then, the growth accelerating since 2005 [234].  The information may have been right in its time, but it’s now outdated.

Secondly, Dr Leaf paraphrases by saying that hereditary factors account for only 5% of cancer and cardiovascular disease.  But Prof Willett didn’t say that at all.  He said that less than 5% of major cancers and coronary heart disease were due to highly penetrant mutations.  Low penetrance polymorphisms of multiple genes account for a significant percentage of risk for cancers and cardiovascular risk (see below).  Broadening the quote by changing the wording is blatantly misleading.

I will cover this in more detail soon, but looking at the latest gene x environment studies for cancer and cardiovascular diseases shows genetics has a rough average influence of 50%.  Claiming that only 5% of cancer and cardiovascular disease is caused by hereditary factors is nonsense.

“According to the American Institute of health, it has been estimated that 75 – 90% of all visits to primary care physicians are for stress related problems ( Some of the latest stress statistics causing illness as a result of toxic thinking can be found at:”

As a researcher, Dr Leaf should be aware of the levels of evidence [240].  The levels of evidence is essentially a grading scheme for classifying scientific research and opinion from the strongest, most rigorous (Level I-1, Meta-analysis of multiple quality randomised controlled trials, like a Cochrane Review) through seven different levels to the weakest form of evidence (Level IV, Anecdotal, which are essentially stories and opinion, “… someone once told me …”)

Websites that are politically, ideologically or financially motivated are, on the ladder of credibility, down on the bottom rung.  They are not peer reviewed to systematically remove biased material.  University or official government health sites like the CDC in America or the NHMRC in Australia offer stronger evidence, and are often worth noting.  Some other health websites like the Better Health Channel ( are valid sources of information, provided that they cite their sources so they can be scrutinized.

But unfortunately, sites like and are examples of strong subject bias.  Citing them as sources of opinion is fair, but citing them as sources of fact is not.  These websites are not independently peer-reviewed, and both suffer from a blatant pro-stress bias.

Offering them as factual evidence demonstrates either sloppy science or intellectual dishonesty.

“Dr H.F. Nijhout (Metaphors and the Role of Genes and Development, 1990) genes control biology and not the other way around.”

Dr Leaf contradicts herself again.  After spending most of the first part of chapter 1 of “Switch On Your Brain” stating that we weren’t victims of our genes or our biology, this quote sounds like she is saying the opposite.  Is Dr Leaf saying that genes DO control development, and by logical extension, we are controlled by our biology?  Or has she misquoted again?

In actual fact, Dr Leaf is playing Chinese Whispers[1] by trying to quote from a secondary source.  Bruce Lipton quoted Dr Nijhout in “Biology of Belief.” [235: p21-2] Looking back at Lipton’s version, it appears that Dr Leaf has “quoted” Dr Nijhout but actually ended up taking a phrase from Dr Lipton’s paragraph on Dr Nijhout.

The value of Dr Nijhout’s quote to Dr Leaf’s theory is questionable.  Lipton quoted Nijhout because Nijhout was suggesting that most scientists have too high a regard for a particular model of gene switching and activity.  But whether scientists have a mildly unrealistic view of the power of genes does not, in anyway, prove that 75 to 98% of all diseases are related to our thoughts.  Nijhout says nothing about thoughts or disease.  His discussion was about a model of gene activity and switching, and not the effects of thought on the genes themselves.

So overall, Dr Leaf’s cited evidence is so weak as to be useless.  Of the seven sources that she cites, one is thirty years out of date, one is ten years out of date and misquoted, one links to websites which are clearly biased, one is a misquote of a misquote that isn’t even relevant, one directly contradicts her twice, another provides a value that is exaggerated and vague, and the other is a hyperbolic exaggeration of an already distorted view of science written by an agnostic cell biologist who has embraced pseudoscience.

Dr Leaf’s statement that “75 to 98 percent of mental and physical illness comes from ones thought life” is baseless.

Evidence contradicting Dr Leaf

So the scientific basis for Dr Leaf’s statement is paper-thin.  What does modern peer-reviewed scientific literature say about the influence of thought on our health?

When considered in the global and historical context [241], the vast majority of illness is related to preventable diseases that are so rare in the modern western world because of generations of high quality public health and medical care.

In a recent peer-reviewed publication, Mara et al state, “At any given time close to half of the urban populations of Africa, Asia, and Latin America have a disease associated with poor sanitation, hygiene, and water.” [242] Bartram and Cairncross write that “While rarely discussed alongside the ‘big three’ attention-seekers of the international public health community—HIV/AIDS, tuberculosis, and malaria—one disease alone kills more young children each year than all three combined. It is diarrhoea, and the key to its control is hygiene, sanitation, and water.” [243] Hunter et al state that, “diarrhoeal disease is the second most common contributor to the disease burden in developing countries (as measured by disability-adjusted life years (DALYs)), and poor-quality drinking water is an important risk factor for diarrhoea.” [244]

Diarrhoeal disease in the developing world - the second most common contributor to disease in these countries, afflicting half of their population - has nothing to do with thought.  It’s related to the provision of toilets and clean running water.

We live in a society that prevents half of our illnesses because of internal plumbing.  Thoughts seem to significantly contribute to disease because we are protected from common diseases affecting the rest of the world - illnesses prevented by our clean water and sewerage systems.  Remove those protective factors and thought no longer appears so significant.

In the same manner, modern medicine has become so good at preventing diseases that thought may seem to be a major contributor, when in actual fact, most of the work in keeping us all alive has nothing to do with our own thought processes.  Like sanitation and clean water, the population wide practices of vaccination and health screening such as pap smears, have significantly reduced the impact of preventable disease.

In the global context, “Recent estimates of the global incidence of disease suggest that communicable diseases account for approximately 19% of global deaths” and that “2.5 million deaths of children annually (are) from vaccine-preventable diseases.” [245] Again, that’s a lot of deaths that are not related to thought life.

Since 1932, vaccinations in Australia have reduced the death rate from vaccine-preventable diseases by 99% [246].  Epidemiological evidence shows that when vaccine rates increase, sickness from communicable disease decreases [247: Fig 2, p52 & Fig 8, p67].

Population based screening has also lead to a reduction in disease and death, especially in the case of population screening by pap smears for cervical cancer.  Canadian public health has some of the best historical figures on pap smear screening and cervical cancer. In Canada, as the population rate of pap smear screening increased, the death rate of women from cervical cancer decreased.  Overall, pap smear screening decreased the death rate from cervical cancer by 83%, from a peak of 13.5/100,000 in 1952 to only 2.2/100,000 in 2006, despite an increase in the population and at-risk behaviours for HPV infection (the major risk factor for cervical cancer) [248].

Around the world, the other major cause of preventable death is death in childbirth.  The risk of a woman dying in childbirth is a staggering one in six for countries like Afghanistan [249] which is the same as your odds playing Russian Roulette.  That’s compared to a maternal death rate of one in 30,000 in countries like Sweden.  The marked disparity is not related to the thought life of Afghani women in labour.  Countries that have a low maternal death rate all have professional midwifery care at birth.  Further improvements occur because of better access to hospital care, use of antibiotics, better surgical techniques, and universal access to the health system [249].  Again, unless one’s thought life directly changes the odds of a midwife appearing to help you deliver your baby, toxic thoughts are irrelevant as a cause of illness and death.

Unfortunately for Dr Leaf, her statement that “75 to 98 percent of mental, physical and behavioural illnesses come from ones thought life” is a myth, a gross misrepresentation of the association of stress and illness.

In the global and historical context of human health, the majority of illness is caused by infectious disease, driven by a lack of infrastructure, public health programs and nursing and medical care.  To us in the wealthy, resource-rich western world, it may seem that our thought life has a significant effect on our health.  That’s only because we have midwives, hospitals, public health programs and internal plumbing, which stop the majority of death and disease before they have a chance to start.

Unless midwives and toilets are the direct result of our thinking, Dr Leaf’s statement is invalid in the global context of health and disease.

What Dr Leaf should have said

Dr Leaf’s assertion is baseless, and is contradicted by global health data.  What then would be a more accurate statement?  How could she correct her assertion to bring it in line with the best medical evidence available?

A better statement would be, “Up to seventy-five percent of mental and physical illness comes from poverty and genetics.”

We have already seen from the global data from the WHO [241] and from authors such as Mara et al, Bartram and Cairncross and Hunter et al that the lack of sanitation and clean drinking water is a significant contributor to global illness [242-244], as is the lack of widespread vaccination programs across the developing nations [245], the lack of public health programs like cervical screening, and the poor access to midwifery care and hospitals [249].  I’m not going to labour the point any further, but suffice to say, the bulk of the global burden of disease is related to poverty throughout the developing world.

When poverty-related diseases are taken out of the picture, as is the situation in the first world, the main contributing factor becomes genetics.

Since 2005, new techniques for gene sequencing have revealed multiple genes, each with an individually minor effect, but when combined, significantly contribute to the risk of developing particular diseases.  Gene x Environment studies use a variety of techniques to deduce the separate contribution that genes and environmental factors have on the risk of developing a disease, or on the risk factors for a disease.

For example, here is a summary of the risk factors for cardiovascular disease and their genetic susceptibility.

HIGH CHOLESTEROL - Genetic susceptibility accounts for 40-60% of the risk for high cholesterol [191].
DIABETES - Genetic factors account for 88% of the risk for type 1 diabetes [95].  There is a strong genetic component of the risk of type 2 diabetes with 62-70% being attributable to genetics [194, 195].
SMOKING - nicotine addiction has a strong hereditary link (50-75% genetic susceptibility) [202].
HYPERTENSION - While part of a much greater mix of variables, genetics are still thought to contribute between 30% and 50% to the risk of developing high blood pressure [204].

It’s clear that environmental variables play a significant part in the risk of developing these traits.  However, it’s also clear that the current evidence points to a much greater genetic contribution, usually greater than 50% of each factor listed.

Similarly for cancer, the effect of genes on the risk of developing most cancers is usually around 50%.  I’ve summarised the recognised Gene x Environment interactions of the four most prevalent types of cancer (as per the review “Cancer Statistics 2013” [206]).

PROSTATE - There are only two risk factors for prostate cancer, familial aggregation and ethnic origin. No dietary or environmental cause has yet been identified [207].  It is most likely caused by multiple genes at various locations in the genome [208].
BREAST - Genes make up 25% of the risk factors for breast cancer, and significantly interacted with parity (parity is the number of children born to a woman) [250].
LUNG/BRONCHUS - Lung cancer is almost exclusively linked to smoking, but nicotine addiction, has a strong hereditary link (50-75% genetic susceptibility) [202] with modest genetic effects noted for smoking initiation and smoking cessation [201].
COLORECTUM - Approximately one third of colorectal cancer is genetically linked [251].


So in summary, Dr Leaf first asserted that “A massive body of research collectively shows that up to 80% of physical, emotional and mental health issues today could be a direct result of our thought lives” but failed to cite any credible scientific evidence to support her claim.

She revised her figures and her quote, asserting that, “75 to 98 percent of mental and physical illness comes from one’s thought life.”  But on closer inspection of both her cited evidence and the scientific data on illness in the global context, her statement is proven to be a gross misrepresentation of the association of stress and illness.

In reality, the majority of mental and physical illness across the spectrum of human existence is related to poverty and genetics, neither of which is related to ones thought life.

[1] I’m not sure if there is a less racist name for this game, but when I was a cub scout, we would sit in a large circle and the original message would be sequentially whispered from one boy to the next, each step degrading the message so that the end product sounded nothing like the original.