For more info, read Supplements for Dog Cardiovascular Health
Canine Heart Disease and the Benefits of L-Carnitine Supplementation
The two main causes of heart failure in dogs is chronic valve disease
and dilated cardiomyopathy. Chronic valve disease frequently leads to
congestive heart failure, affecting between 11 and 42% of dogs. In aged
dogs the incidence rate is above 60%. Chronic valve disease affects
primarily small to medium-sized doges, e.g., Spaniels and Dachshunds.
Larger dogs, like German Shepards and Doberman pinschers, tend to suffer
more from dilated cardiomyopathy (enlarged heart). Dilated
cardiomyopathy is a progressive form of heart disease that develops
slowly over the life of the dog, often without obvious symptoms, and can
lead to the development of cardiac decompensation (inadequate
circulation) and congestive heart failure later in life (6 to 10 years).
Dilated cardiomyopathy is characterized by depressed systolic and
diastolic pressure in the left ventricle, compensatory hypertrophy (cell
size expansion), dilation of the left ventricle, and increased systemic
vascular resistance. With time, as the severity of the disease
increases, the left ventricle will undergo remodeling that results in a
thinner, and thus weaker ventricular wall. By the time this occurs the
disease is well advanced.
The symptoms of heart disease in dogs include sluggishness, despondency,
weakness, unexplained weight loss, easily out of breath, a
progressively worsening cough, or collapse. Any of these symptoms should
trigger a visit to a veterinarian sooner rather than later, because
effective treatments are available that can improve the health and
prolong the life of the dog. In addition to the treatment regimen
suggested by the veterinarian, supplementation with L-carnitine should
also be discussed because research studies have shown positive benefits
if combined with traditional treatments; L-carnitine supplementation can
lower the amount and number of prescription heart medications a dog may
have to take. L-carnitine supplementation may also be able to slow,
arrest, or even in rare cases, partially reverse heart disease. There
have also been some reports of delayed disease onset when L-carnitine
supplementation is begun early in life, well before disease symptoms
have appeared.
L-Carnitine is Essential to Proper Cardiac and Skeletal Muscle Function
The amino acid L-carnitine is normally synthesized in the liver of
healthy animals by an enzymatic process that relies on the essential
amino acids lysine and methionine. Once synthesized, the blood supply
carries L-carnitine to cells and tissues throughout the body where it
assists in the breakdown of fatty acids for energy. L-carnitine performs
this function by binding to the surface of an intracellular organelle
called mitochondria, the primary energy producing factories in our
bodies. Once L-carnitine binds to this membrane it assists in the
transport of fatty acids across the membrane where it is oxidized
(broken down) by oxygen to produce energy.
The primary consumers of L-carnitine at the cellular level are the
skeletal and cardiac muscles, and between 95 and 98% of the body’s
L-carnitine is stored in these muscles. Muscle cells are also packed
with mitochondria if the animal doesn’t live a sedentary lifestyle. A
breakdown at any point in this cycle, whether diet or disease related,
will cause rapid fatigue when muscles are exerted because the
mitochondria in the muscles are forced to switch from the more efficient
aerobic metabolic cycle that depends on fatty acids and oxygen, to an
anaerobic metabolic cycle that depends primarily on glucose. In the
presence of low L-carnitine concentrations muscle cells will be unable
to keep up with demand, resulting in weakness and fatigue. For this
reason, L-carnitine supplementation can provide a natural,
non-prescription, and non-toxic buffer against rapid cardiac muscle
fatigue.
A prominent hypothesis that was put forward years ago argues that heart
disease progression occurs in part because the fatty acid metabolic
cycle is dysfunctional. This was observed repeatedly in patients with
severe heart disease, but more recent studies have shown that fatty acid
metabolism in moderately and less severe heart disease patients is
actually normal by all known measurements. Fatty acid metabolic
dysfunction is therefore unlikely to be a causative factor for heart
disease. Recent studies are beginning to show that metabolic dysfunction
in heart disease patients is much more complex than previously thought
and there may be still undiscovered pathways and molecules that could
help explain disease onset and progression. L-carnitine supplementation
may therefore be an effective treatment for canine heart disease because
it ensures heart muscles have access to sufficient energy despite the
presence of disease.
The needed dosage for prevention is 100-200 mg twice per day. To help reverse heart problems, the recommended dosage is close 1000-2000 mg twice per day.
L-Carnitine Supplementation and Adolescent Dogs
Under normal circumstances a healthy liver and diet are sufficient to
maintain the fatty acid cycle properly. Red meat is an excellent source
of L-carnitine, providing anywhere from 500 to 2000 mg of L-carnitine
per kg. By comparison, vegetables contain only trace amounts of this
amino acid. A diet poor in L-carnitine isn’t really a concern in healthy
animals though, because the liver can produce enough to sustain normal
function if the diet contains sufficient amounts of the amino acids
lysine and methionine.
There may be an exception to the above statement when considering
developing pups. Newborn pups rapidly ramp up their fatty acid metabolic
cycle to near adult levels within 24 hours, and this is maintained
during the suckling period. Once weaned, the L-carnitine levels fall
well below the levels needed for full use of the fatty acid metabolic
cycle and remain low until adulthood. By comparison, the liver and blood
of adult dogs contains enough L-carnitine to fully activate the fatty
acid metabolic cycle several times over. Supplementing the diet of
weaned, adolescent dogs with L-carnitine may therefore provide an edge
if the diet isn’t already rich in meat. Whether or not to supplement the
diet of adolescent dogs with L-carnitine, and an appropriate dosage, is
a decision that should be arrived at through discussions with a trusted
veterinarian.
L-Carnitine Supplementation and Cognitive Decline
As we age we may experience a decline in cognitive abilities. Dogs are
no exception. The decline could be the result of brain pathology,
circulatory problems (heart disease), or just plain getting old. Current
theories suggest cognitive decline due to normal aging may be related
to decreased mitochondrial function. Since mitochondria depend so
heavily on L-carnitine to produce energy, a reasonable expectation would
be that diet supplementation may slow cognitive decline in aged dogs by
providing metabolic support for mitochondria in the brain. When the
diet of aged dogs was supplemented with α–lipoic acid and L-carnitine
for several months, significant improvements in cognitive function were
observed.
Summary
The research studies reviewed here are consistent with what is known
about diet requirements for dogs. A diet rich in meat provides
sufficient L-carnitine for healthy dogs, and this may be especially
important for adolescent dogs. If the quality of the diet is in
question, L-carnitine supplementation may help forestall or slow the
onset of heart disease and maintain healthy muscle function. In dogs
with heart disease, L-carnitine supplementation may provide some relief
from the symptoms of disease and lower the amount of medications that
are required. In older dogs L-carnitine supplementation may help improve
cognitive abilities. The dosage that is decided upon will depend on the
quality of the diet, the dog’s state of health, and discussions with a
trusted veterinarian.
