Cancer is the second biggest killer of children, largely because they are even more susceptible than adults to the growing number of poisons in our lives.
Childhood cancer is on the rise, and medical science says that the reason remains a mystery.
Cancer is a multifactoral disease. But, while scientists continue to focus their research on the genetic links to childhood cancer, important environmental triggers - vaccines, pesticides, food additives and electromagnetic radiation - are all but ignored.
Experts continue to decry that cancer is rare in children, yet statistics show that, after accidents, childhood cancer is the second biggest killer of children in the US (Am Fam Physician, 2000; 61: 2144-54). Government figures suggest the same is true in the UK (see National Statistics, Mortality Statistics: Child-hood, Infant and Perinatal, London: HMSO, 1999).
Just like adults, children can be prone to cancer at any site in the body. Nevertheless, two sites - bone and brain - are now particularly common. Figures show that acute lymphoblastic leukaemia (ALL) rates have risen 10 per cent in the last 15 years, while the incidence of tumours of the central nervous system are up more than 30 per cent.
Children are many times more vulnerable to the effects of toxic insults than adults, and their response to toxic exposures can also differ markedly. A good example is the paradoxical response to phenobarbital and Ritalin seen in children vs adults. Phenobarbital, a sedative in adults, produces hyperactivity in children. On the other hand, Ritalin, used as an antihyperactive drug in children, has the opposite effect in adults.
There are many reasons for this paradoxical response (see box below). Differences in the developing infant and child affect the absorption, dose, distribution, metabolism, storage and excretion of chemicals or drugs in the body and, therefore, their toxicity (see R.J. Roberts' overview in Similarities and Differences Between Children and Adults, Guzelian PS et al. (eds), Washington, DC: ILSI Press, 1992; 11-5).
The efficiency and availability of metabolic enzymes varies with age (Environ Health Perspect, 1995; 103 [Suppl 6]: 7-12), which can result in differences in sensitivity to the toxic effects of both drugs and environmental toxins.
But perhaps the most influential characteristic of infants and children is that they are still growing and developing. During childhood, different systems and organs develop at different rates and at different times. Growing tissue may be more sensitive to toxic insults than other tissue. Studies of exposure to cigarette smoke have shown that the risk of dying of breast cancer is greater for those who started smoking before age 16 than for those who started after age 20 (Am J Epidemiol, 1994; 139: 1001-7).
Studies of the effects of radiation also suggest an increased susceptibility in those exposed during childhood. Among survivors of the atomic bomb in Hiroshima and Nagasaki, Japan, susceptibility to leukaemia was greater for those who were under 20 when exposed compared with those who were older. Moreover, the type of leukaemia varied according to the age at exposure (Environ Health Perspect, 1995; 103 [Suppl 6]: 41-4).
Pesticides kill things
In homes, schools and gardens, in their food and water, and in the air they breathe, children are bombarded by pesticides. Despite the objections of major chemical companies, the link between pesticide exposure and childhood cancer is firmly established (Environ Health Perspect, 1997; 105: 1068-77; Am J Epidemiol, 2000; 151: 639-46; Cancer, 2000; 89: 2315-21; Eur J Cancer, 1996; 32A: 1943-8; Environ Res, 1980; 23: 257-63).
Case reports and case-control studies have linked pesticides to a wide range of malignancies, including leukaemia, non-Hodgkin's lymphoma, neuroblastoma and Wilms' tumour, as well as cancers of the brain, colorectum and testes (Environ Health Perspect, 1998; 106 [Suppl 3]: 893-908).
Research has shown that pesticide use in the home - to get rid of termites, flies and wasps, no-pest strips, flea collars, and garden insecticides and herbicides - has resulted in a significant increase in childhood brain cancer (Arch Environ Contam Toxicol, 1993; 24: 87-92).
In one study, the risk of childhood leukaemia increased nearly four times when pesticides were used indoors at least once a week, and more than six times when garden pesticides were used at least once a month (J Natl Cancer Inst, 1987; 79: 39-46).
Another study suggested that children living in homes with pest strips (imbedded with insecticides) had one-and-a-half to three times the risk of developing leukaemia than those living in homes without strips. Even worse, children under 14 had four times the normal risk of connective tissue tumours if their gardens are treated with pesticides or herbicides (Am J Public Health, 1995; 85: 249-52).
Shots in the dark
The efficacy and necessity of childhood vaccinations continues to be one of the more emotive subjects in medicine. While officials continue to debate the connection between behavioural and learning disorders and vaccination, other potentially deadly effects of vaccination have been shoved into the background. Indeed, how many parents have ever considered whether childhood vaccinations might also lead to childhood cancer?
Little research has been carried out in this area. One study concluded that there is no risk. However, the study population was small (less then 900 children) and not all children received the same number of vaccinations. Other flaws in the study design suggest that its results are not conclusive (Br J Cancer, 1999; 81: 175-8).
No study has looked at children who have had their full complement of vaccinations and developed cancer, and compared them with children who have had few or no jabs. In addition, none of the childhood vaccines currently in use has ever been tested for carcinogenic potential (see Physicians' Desk Reference, 51st edn, Medical Economics Inc, 1997).
The truth is, we don't know whether vaccines can cause cancer. But there are several sound reasons why they might. The manufacture of vaccines is a filthy process. The viruses are gathered from the excrement and bodily fluids of infected individuals. Once gathered, it is grown in a toxic medium, as disease-causing organisms cannot live in a 'healthy' medium (just as they cannot proliferate in a healthy body).
These are further mixed with other toxins, including formaldehyde (a carcinogen) to inactivate them, aluminium and the mercury derivative thimerosal (both carcinogens), phenol (yet another carcinogen) and antibiotics.
In addition, viruses themselves may cause cancer, and the process by which viruses are 'inactivated' for use in vaccines is not infallible. A well-known example of this is the simian virus 40 (SV40) that contaminated the early Salk polio vaccine. SV40 was a carcinogenic virus growing on the monkey kidneys used to culture poliovirus. It was discovered only after hundreds of thousands of individuals had been injected with it. Not only was this virus responsible for cancer in the vaccine recipients, but it was associated with DNA damage passed on through sexual contact as well as to their unborn children. Evidence of SV40 is still being found in brain tumours today (J Natl Cancer Inst, 1995; 87: 1331; Brain Pathol, 1999; 9: 33-42).
The unhealthy vitamin
Concern has also been raised as to whether injections of vitamin K given immediately after birth increase the risk of childhood cancer. In 1990, a positive association was found between the vitamin K jab and childhood leukaemia. The study involved 597 children in England and Wales born between 1968 and 1985, and diagnosed with cancer between 1969 and 1986, and a matching group of children who didn't have cancer.
The association between overall cancer incidence and intramuscular vitamin K was small. However, there was a strong association with the incidence of leukaemia. The authors concluded that '. . . the risk, if any, attributable to the use of vitamin K cannot be large, but the possibility that there is some risk cannot be excluded' (Br J Cancer, 1990; 62: 304-8).
Eight years and a great deal of debate later, the British Medical Journal devoted an entire issue to vitamin K injections and its link with cancer. An editorial likened the subject to a 'Gordian knot' that still awaits untying (BMJ, 1998; 316: 161-2). One of the studies found no association (BMJ, 1998; 316: 184-9), but others felt otherwise. 'The possibility that there is some risk cannot be excluded,' concluded one (BMJ, 1998; 316: 178-84).
A third study looking at British children who developed cancer before age 15 found no association between intramuscular vitamin K and all childhood cancers and leukaemia. But once again, there was a raised risk for leukaemia developing one to six years after birth.
The researchers concluded, 'It is not possible, on the basis of currently published evidence, to refute the suggestion that neonatal intramuscular vitamin K administration increases the risk of early childhood leukaemia' (BMJ, 1998; 316: 189-93). The most recent review of the vitamin K-cancer link arrived at much the same conclusion (Br J Cancer, 2002; 86: 63-9).
Are kids electric?
Evidence is also accumulating to show that living near even relatively low levels of electromagnetic field (EMF) radiation from mains electricity or powerlines can significantly raise a child's chances of developing leukaemia. In 1979, the first major study linking such EMFs to childhood cancer was published (Am J Epidemiol, 1979; 109: 273-84).
Other studies followed, including a Swedish study of some half a million people showing that children exposed to varying levels of household EMFs had up to a fourfold greater risk of developing leukaemia (Am J Epidemiol, 1993; 138: 467-81). Others have also confirmed the EMF-cancer link (Eur J Cancer, 1995; 31A: 2035-9; Lancet, 1993; 342: 1295-6; Am J Epidemiol, 1991; 134: 923-7; Am J Epidemiol, 1988; 128: 21-38).
Most recently, however, back-to-back UK studies on electrical powerlines and cancer reached mixed conclusions. One, by Professor Denis Henshaw of Bristol University's Human Radiation Effects Group, took 2000 field measurements and found that the toxic effects of EMFs could extend up to more than 100 yards (91 metres) on either side of powerlines.
He also suggested how EMFs could cause cancer. According to Henshaw, living near powerlines with radiation levels dozens of times the legal limit may indirectly cause cancer by increasing the concentration of carcinogenic airborne particles that are produced naturally in the soil and by local traffic pollution (Int J Radiat Biol, 1999; 75: 1505-21). This conclusion supports earlier research showing potentially toxic interactions between alternating EMFs surrounding powerlines and radioactive breakdown products of naturally occurring radon gas (Int J Radiat Biol, 1996; 69: 25-38).
However, the UK Childhood Cancer Study - an 18-year study of EMFs and 2226 cancer-stricken children matched with healthy children - did not support a link between EMF exposure and childhood cancer (Lancet, 1999; 354: 1925-31).
Nevertheless, the authors noted that the study design may have been flawed (an admission omitted from most of the media reporting). A non-relevant criterion was used, and only 2.3 per cent of the studied children fell into the higher-exposure category. Exposure was also not comparable to studies in other countries, such as North America, where the voltage is different and rates of high exposure are greater. Another study in New Zealand (Lancet, 1999; 354: 1967-8) also proved inconclusive, but had the same design flaws as the UKCCS.
Overall, we know pitifully little about the role of environmental carcinogens in childhood cancer (Environ Health Perspect, 1998; 106 [Suppl 3]: 875-80). When studies have been done, scientists have tended to hedge their bets by concluding that the effects on the general population are likely to be small. But add up all these small effects and there may be a strong case for an environmental cause for some childhood cancers.
Also, whereas scientists now believe that many adult cancers are due to lifestyle factors such as smoking, diet, occupation, and exposure to radiation and toxic chemicals, medical science has consistently failed to give the same consideration to childhood cancers.
The average age for a diagnosis of childhood cancer is six years, yet children often have more advanced cancer at first diagnosis. Only about 10 per cent of adults show evidence of spreading disease when first diagnosed compared with 80 per cent in children.
Doctors say that such late diagnosis is because the symptoms of cancer mimic so many other childhood illnesses (Am Fam Physician, 2000; 61: 2144-54). However, another viewpoint is that many medics, believing that childhood cancer is rare, may not take the symptoms seriously and may see exploratory tests for youngsters as unnecessary.
In the US, Alexander Horwin died of the most common form of brain cancer - medulloblastoma - after his parents were told repeatedly by their paediatrician that he had a 'virus'. His parents have since made a herculean effort to raise awareness of the potential links between childhood vaccinations and cancer (log on to www.ouralexander for details).
Perhaps our children's increased vulnerability in the face of environmental risk factors combined with the alarming increase in the incidence of childhood cancer is our wake-up call, urging us to take the unique biology of children and the damaging potential of these environmental insults even more seriously.
Where cancer is concerned, the best form of cure is prevention, and it behooves us to do whatever we can to ensure that our children have the resources to remain healthy in a toxic world.