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Biomedical subjects

A J Christophers

Publications and source records attributed to A J Christophers.

12 recordsLinked to original sources
PubMed1998

Melanoma is not caused by sunlight.

When comparisons are made of cutaneous melanoma with cutaneous squamous cell cancer (SCC) and basal cell cancer (BCC) of the skin with respect to age dependence, sex ratio, distribution on the body, association with sun exposure, and variation with latitude, it is clear that SCC is due almost entirely to sun exposure, that BCC is partly due to sun exposure, and that melanoma is not due to sun exposure. For melanoma, it is only latitudinal variation that favours the hypothesis of sun exposure causation. However, an examination of the latitudinal variation of SCC incidence reveals that this is several fold greater than can be accounted for by variation of exposure to UV-B. The other factor operating appears to be skin temperature. For melanoma, it is postulated that the latter factor by itself may suffice to account for the observed variation with latitude. The higher incidence of melanoma in the higher social classes and its increasing incidence with age may be readily explained by the hypothesis that melanoma incidence increases with increase in skin temperature.

Adult↗
PubMed1997

Lead exposure and children's intelligence: do low levels of lead in blood cause mental deficit?

OBJECTIVE: It has come to be generally accepted that low levels of lead exposure may result in mental deficit. This causal inference is based on claimed time precedence of the lead exposure and on biological plausibility. The objective of this study is to argue that mental deficit causes pica which causes lead exposure (i.e. to support the theory of reverse causation). METHODOLOGY: The literature since the 1930s has been interpreted in the light of our own long experience in the investigation of lead exposure in children and adults to support the arguments in favour of reverse causation. RESULTS: The arguments for reverse causation are based on: (i) analogy with mental retardation which causes increased lead exposure; (ii) the results of published prospective studies that show a special relationship between blood lead levels at 24 months and intelligence tested later, exactly what would be predicted by the reverse causation theory; and (iii) on an alternative explanation for mental retardation following lead encephalopathy (i.e. that mental retardation following encephalopathy is due to anoxia and not due to a direct destructive effect on the brain neurones). The arguments, which have been proposed for the conventional view, are rejected for the following reasons: (i) none of the prospective studies have found a relationship between cord blood lead levels and intelligence tested later, undermining the argument based on time precedence of lead exposure; and (ii) there is no convincing evidence that lead poisoning, short of encephalopathy, causes mental retardation. CONCLUSION: We believe that the reverse causation hypothesis is a more plausible explanation of the facts.

Causality↗
PubMed1992

Phenoxy herbicides and chlorophenols: a case control study on soft tissue sarcoma and malignant lymphoma.

A case control study on patients with soft tissue sarcoma and malignant lymphoma was undertaken to test whether there was any association between these diseases and past exposure to chlorinated phenoxy acid herbicides or chlorophenols. It was carried out over the period 1982-1988 in Victoria, Australia. Thirty males with soft tissue sarcoma and 52 males with malignant lymphoma were matched by age, place of residence and sex with one population control and one cancer control each. Exposure was assessed by personal interviews conducted by an occupational hygienist. Exposures within 5 years prior to diagnosis of each matched case were ignored, both for the cases and their matched controls. The estimated relative risks for definite or probable exposure to chlorinated phenoxy compounds or chlorophenols for at least 1 day were 1.0 (95% confidence interval (CI): 0.3-3.1) for soft tissue sarcoma and 1.5 (95% CI: 0.6-3.7) for malignant lymphoma. When the criterion for exposure was raised to more than 30 days, the estimated relative risks were 2.0 (95% CI: 0.5-8.0) for soft tissue sarcoma and 2.7 (95% CI: 0.7-9.6) for malignant lymphoma. Additional analyses were carried out for exposure of at least 1 day to phenoxy herbicides alone or chlorophenols alone. None of the estimated relative risks was significantly greater than unity.

Adult↗
PubMed1977

Industrial lead poisoning and the family physician.

According to Health Department Regulations, lead workers are required to undergo periodical medical examinations to determine their fitness for work. These examinations are supervised by the Industrial Hygiene Division which can assist any practitioner with a patient thought to have had excessive exposure to lead.

Australia↗