CATS, DOGS, AND
CADMIUM: POSSIBLE CHRONIC POISONING
By Dr. Michael W. Fox
“Cumulative
exposure to cadmium has been associated with
elevations in blood pressure and renal dysfunction in human beings and rodents”.
This introductory statement in a paper entitled “Association
of urinary cadmium excretion with feline hypertension” by N.C. Finch, H. M.
Syme and J. Elliot (1) from my alma mater, the Royal
Veterinary College London, raises an important question. Other than cigarette
smoke, possible environmental sources of cadmium in afflicted cats were not identified or
suggested by these authors. They
acknowledged that hypertension caused by kidney disease could increase cadmium
excretion in the urine, but that there was no relationship between renal
function and cadmium excretion. Furthermore, causality could not be inferred in
so far as cadmium causing hypertension or hypertension resulting in more
cadmium being excreted.
Suffice it to say,
hypertension in cats, as in humans and
other animals, must be controlled to prevent damage to the eyes, heart, kidneys
and other internal organs, and the findings of this clinical research study
calls for a full assessment of cadmium levels in manufactured cat foods.
I recall over 30
years ago that the U.S. Department of
Agriculture expressed concern over humans consuming the livers of slaughtered
laying hens because of high cadmium levels. Cadmium residues in the livers of
aged beef and dairy cattle were also a concern in some European countries at
that time. Today, state authorities from Alaska to Main advise moose hunters
not to eat the livers and kidneys of mature bulls because of high cadmium
levels acquired from consuming willow and other vegetation that concentrate cadmium
present in various soils. Human and domestic animal sources of cadmium include
crop contamination from various soils and chemical fertilizers and from cadmium
being concentrated in consumed animal parts (see below)...
According
to Health Canada
(www.hc.gc.ca) “A
maximum acceptable concentration of 0.005 mg/L (5 µg/L) for
cadmium in drinking water has been established for humans on the basis of
health considerations. Food is the main source of cadmium intake for individuals
who are not occupationally exposed. A joint FAO/WHO expert committee has
estimated a provisional tolerable weekly intake of cadmium for an adult to be
from 0.4 to 0.5 mg. Because it would be difficult to reduce cadmium intake in
food, intake from water should be as low as possible. Certain shellfish, such
as crabs and oysters, may concentrate cadmium to extremely high levels in
certain tissues, even if they inhabit waters containing low levels of cadmium.
Cadmium may also concentrate in the kidney and liver of swine, sheep, and
cattle (2). Reported concentrations of cadmium in foodstuffs vary widely;
concentrations in most foods average about 0.05 mg/kg on a wet-weight basis
(3). Concentrations in beef livers, kidneys, and brown crabmeat can reach 0.2,
1.6, and 21.0 mg/kg, respectively (4). More
detailed data are available from the national food monitoring program of the
Department of National Health and Welfare,
( Department of National Health and Welfare.
Unpublished data, Health Protection Branch, Ottawa 1978). Average cadmium concentrations,
on a
fresh-weight edible part basis, ranged from 0.1 (0.01 to 0.13) mg/kg for meat
and poultry to 0.60 (0.13 to 2.78) mg/kg for beef kidney. Of the 16 food types
listed, a mean concentration of 0.05 mg/kg was exceeded in beef (0.6 mg/kg) and
pork (0.26 mg/kg) kidneys, and in beef (0.15 mg/kg),
pork (0.09 mg/kg), and chicken (0.06 mg/kg) livers.
One analysis of pet foods-- SpexCertiPrep,
a laboratory standards company, "Trace Metal
Analysis of Commercial Pet Food
for Toxic Metals by ICP and ICP-MS." By R. Obenauf et al
(www.spexcsp.com) reported:
pet food levels of cadmuim ranged from 1.8-130 parts per
billion with a mean of 42 compared to human grade tuna at 36, sardines at 14
and chicken at 1.8 ppb. Toxic metal levels were gnerally higher in dry versus
canned cat and dog foods. ( 1 ppb= 1 microgram/Kg or 0.001 mg/Kg).
According
to EVISA (5) “Cadmium appears to be the largest single contributor to
autoimmune thyroid disease. It is a very powerful and toxic metal which
seems to be placed at the very center of the thyroid story ---Not only
does cadmium appear to play a very pivotal role in thyroid disease, it is a
very unique mineral. It is extremely toxic and has toxic biological effects at
concentrations smaller than almost any commonly found mineral. Despite this
great toxicity, there is some evidence that cadmium is an essential nutrient
with biological function. One of the
greatest effects of cadmium is that it depletes selenium in the body because
selenium is essential for cadmium removal. Selenium atoms combine with cadmium
atoms and are escorted out of the body via the bile system. When selenium is
depleted by cadmium, there is less selenium to form the deiodinase enzymes
which convert T4 to T3, resulting in low T3 and hypothyroidism. Also there is
less selenium to form glutathione peroxidase, one of the body's prime
antioxidants. This results in greater levels of reactive oxygen species and
hydrogen peroxide, which lead to an increased production of thyroid hormone and
damage to the thyroid gland”.
Dr. W. Jean Dodds sent me an additional
important consideration, writing that:
“A
second mineral of importance to
thyroid function when over-supplemented is iodine. Even though the effect of
iodine deficiency in promoting goiter and hypothyroidism has been known for
decades, one should not automatically supplement a hypothyroid or normal dog’s
diet with iodine. Many people unwittingly do this by feeding extra kelp or seaweed.
This supplementation can result in excessive iodine intake, which can in turn
cause the thyroid gland to overproduce T4 and T3. This then provokes an
immune-mediated response in the body, where the immune system actually attacks
the thyroid gland and inhibits hormone output. Such a response can suppress
thyroid levels by up to 25 percent, causing hypothyroidism as well as
autoimmune thyroiditis (6)”.
These observations from an expert panel of
scientists and scientific publications warrant
closer scrutiny of the roles excess cadmium (and
iodine especially in sea food ingredients in pet foods) may play in the
epidemic of thyroid disease in cats, manifested as hyperthyroidism, and in dogs
as hypothyroidism, many cases being identified as autoimmune thyroid disease.
As a precautionary measure to reduce
consumption of potentially toxic substances (such as cadmium as well as lead,
cobalt, chromium, arsenic, mercury, selenium, copper, fluoride and uranium)
which gradually accumulate in various body parts, the internal organs,
especially livers and kidneys, bones and fats (which can also accumulate
lipophilic pesticides and dioxins) of mature animals should not be recycled
into the human, companion animal and farmed animal (including farmed fish) food
chain. Mature animals-- ‘spent’ breeder-sows and other species kept for
breeding purposes, spent egg-laying hens and also horses, ---should not be
included in pet foods or livestock and fish feed because of this age-related
bio-accumulation of toxic substances .High in the aquatic food-chain
carnivorous fish and long-lived marine life that both concentrate such toxic
chemicals (and also bromide compounds from fire-retardant treated materials and
endocrine disrupting chemicals in plastics that are a major ocean pollutants)
should likewise be considered unfit food items for human and non-human
consumption..
REFERENCES
(1)
Finch,
N.C. et al Association of urinary
cadmium excretion with feline hypertension. Veterinary
Record 170: 125, 2012
(2)
Nordberg,
G.F. Health hazards of environmental cadmium pollution. Ambio, 3: 55 1974
(3)
Dabeka,
R.W. et al Dietary intakes of lead,
cadmium, arsenic and fluoride by Canadian adults: a 24-hour duplicate diet
study. Food Addit. Contam., 4(1): 89
1987
(4)
Chau, Y.K.,
et al Distribution of trace elements and chlorophyll a
in Lake
Ontario. In: Proc. 13th Conf. on Great
Lakes Research. p. 659 1970
(5)
EVISA is
a project funded by the EU under the “GROWTH” programme (G7RT-CT-2002-05112)
EVISA's web portal (www.speciation.net) is the premier information source for
all those interested in trace element determination and speciation. . For
additional references including laboratory studies on animals and human
clinical research, visit www. www.ithyroid.com/cadmium.htm.
(6)
Dodds, W.J.,
Laverdure, D. “The Canine Thyroid Epidemic”.
DogWise Publishing, Ch.
2 & 4, 2011 www.dogwise.com
I
appreciate the helpful comments of Margaret Gates with www.feline-nutrition.org in the
completion of this brief review.
