4 Hidden Dangers of Pork
Written by
Denise Minger
MD, on June 22, 2018
Among foods that inspire a cult-like following, pork often leads the pack, as
evidenced by the
65% of Americans
eager to name bacon the country's national food.
Unfortunately, that popularity comes at a cost. Along with being the most
commonly consumed meat in the world, pork may also be one of the most dangerous,
carrying some important and under-discussed risks that any consumer should be
aware of.
Thanks to the revival of nose-to-tail eating,
offal
has redeemed itself among health enthusiasts, especially liver, which is prized
for its vitamin A content and massive mineral lineup.
But when it comes to pork,
liver
might be risky business.
In developed nations, pork liver is the top food-based transmitter of hepatitis
E, a virus that infects 20 million people each year and can lead to acute
illness (fever, fatigue, jaundice, vomiting, joint pain and stomach pain),
enlarged liver and sometimes liver failure and death
Most hepatitis E cases are stealthily symptom-free, but pregnant women can
experience violent reactions to the virus, including fulminant hepatitis
(rapid-onset liver failure) and a high risk of both maternal and fetal mortality
In fact, mothers who get infected during their third trimester face a death rate
of up to 25%
In rare cases, hepatitis E infection can lead to myocarditis (an inflammatory
heart disease), acute pancreatitis (painful inflammation of the pancreas),
neurological problems (including Guillain-Barré syndrome and neuralgic
amyotrophy), blood disorders and musculoskeletal problems, such as elevated
creatine phosphokinase, indicating muscle damage, and multi-joint pain (in the
form of polyarthralgia)
People with compromised immune systems, including organ transplant recipients on
immunosuppressive therapy and people with HIV, are more likely to suffer from
these severe hepatitis E complications
So, just how alarming are pork's contamination stats? In America, about 1 out of
every 10 store-bought pig livers tests positive for hepatitis E, which is
slightly higher than the 1 in 15 rate in the Netherlands and 1 in 20 rate in the
Czech Republic (. One study in Germany found that about 1 in 5 pork sausages
were contaminated
France's traditional figatellu, a pig liver sausage that's often consumed
raw, is a confirmed hepatitis E carrier. In fact, in regions of France where raw
or rare pork is a common delicacy, over half the local population shows evidence
of hepatitis E infection.
Japan, too, is facing rising hepatitis E concerns as pork gains And in the UK?
Hepatitis E shows up in pork sausages, in pork liver and at pork
slaughterhouses, indicating the potential for widespread exposure among pork
consumers.
It might be tempting to blame the hepatitis E epidemic on commercial farming
practices, but in the case of the pig, wilder doesn't mean safer. Hunted boars,
too, are frequent hepatitis E carriers, capable of passing on the virus to
game-eating humans).
Apart from total pork abstinence, the best way to slash hepatitis E risk is in
the kitchen. This stubborn virus can survive the temperatures of rare-cooked
meat, making high heat the best weapon against infection (19).
For virus deactivation, cooking pork products for at least 20 minutes to an
internal temperature of 71°C (160°F) seems to do the trick
However, fat can protect hepatitis viruses from heat destruction, so fattier
cuts of pork might need extra time or toastier temperatures
Summary:
Pork products, particularly liver, frequently carry hepatitis E, which can cause
severe complications and even death in vulnerable populations. Thorough cooking
is necessary to deactivate the virus.
One of the most surprising risks associated with pork — one that's received
remarkably little airtime — is multiple sclerosis (MS), a devastating autoimmune
condition involving the central nervous system.
The robust link between pork and MS has been known at least since the 1980s,
when researchers analyzed the relationship between per capita pork consumption
and MS across dozens of countries
While pork-averse nations like Israel and India were nearly spared from MS's
degenerative grips, more liberal consumers, such as West Germany and Denmark,
faced sky-high rates.
In fact, when all countries were considered, pork intake and MS showed a
whopping correlation of 0.87 (p<0.001), which is much higher and more
significant than the relationship between MS and fat intake (0.63, p<0.01), MS
and total meat intake (0.61, p<0.01) and MS and beef consumption (no significant
relationship).
For perspective, a similar study of diabetes and per capita sugar intake found a
correlation of just under 0.60 (p<0.001) when analyzing 165 countries.
As with all epidemiological findings, the correlation between pork consumption
and MS can't prove that one causes the other (or even that, within
MS-stricken countries, the most enthusiastic pork consumers were the most
diseased). But as it turns out, the evidence vault goes much deeper.
Earlier, a study of inhabitants of the Orkney and Shetland Islands of Scotland,
a region teeming with unusual delicacies, including seabird eggs, raw milk and
undercooked meat, found only one dietary association with MS — consumption of
"potted head," a dish made from boiled pig's brain
Among Shetland residents, a significantly higher proportion of MS patients had
consumed potted head in their youth, compared to healthy, age and sex-matched
controls (.
This is particularly relevant because — per other research — MS that strikes in
adulthood might stem from environmental exposures during adolescence.
The potential for pig brain to trigger nerve-related autoimmunity isn't just an
observational hunch, either. Between 2007 and 2009, a cluster of 24 pork plant
workers mysteriously fell ill with progressive inflammatory neuropathy,
which is characterized by MS-like symptoms such as fatigue, numbness, tingling
and pain.
The source of the outbreak? So-called "pig brain mist" — tiny particles of brain
tissue blasted into the air during carcass processing.
When workers inhaled these tissue particles, their immune systems, per standard
protocol, formed antibodies against the foreign porcine antigens.
But those antigens happened to bear an uncanny resemblance to certain neural
proteins in humans. And the result was a biological calamity: confused about who
to fight, the workers' immune systems launched a guns-blazing attack on their
own nerve tissue.
Although the resulting autoimmunity wasn't identical to multiple sclerosis, that
same process of molecular mimicry, where foreign antigens and self-antigens are
similar enough to trigger an autoimmune response, has been implicated in the
pathogenesis of MS.
Of course, unlike pig brain mist, hot dogs and ham aren't literally
inhaled (teenage boys notwithstanding). Could pork still transmit problematic
substances through ingestion? The answer is a speculative yes. For one, certain
bacteria, particularly Acinetobacter, are involved in molecular mimicry
with myelin, the nerve-sheathing substance that becomes damaged in MS (.
Although the role of pigs as Acinetobacter carriers hasn't been
exhaustively studied, the bacteria has been found in pig feces, on pig farms and
in bacon, pork salami and ham, where it serves as a spoilage organism (.
If pork acts as a vehicle for Acinetobacter transmission (or in any way
increases the risk of human infection), a link with MS would make sense.
Two, pigs may be silent and under-studied carriers of prions, misfolded
proteins that drive neurodegenerative disorders like Creutzfeldt-Jakob disease
(the human version of mad cow) and Kuru (found among cannibal societies)
Some researchers suggest MS itself could be a prion disease, one that targets
oligodendrocytes, the cells that produce myelin. And since prions — and their
associated diseases— are transmitted by consuming infected nerve tissue, it's
possible that prion-harboring pork products could be one link in the MS chain.
Summary:
A causative role of pork in MS is far from a closed case, but the unusually
strong epidemiological patterns, biological plausibility and documented
experiences make further research imperative.
Liver problems tend to trail closely on the heels of some predictable risk
factors, namely hepatitis B and C infection, exposure to aflatoxin (a carcinogen
produced by mold) and excessive alcohol intake (43,
44,
45).
But buried in the scientific literature is another potential scourge of liver
health — pork.
For decades, pork consumption has faithfully echoed liver cancer and cirrhosis
rates around the world. In multi-country analyses, the correlation between pork
and cirrhosis mortality clocked in at 0.40 (p<0.05) using 1965 data, 0.89
(p<0.01) using mid-1970s data, 0.68 (p=0.003) using 1996 data and 0.83 (p=0.000)
using 2003 data
).
In those same analyses, among the 10 Canadian provinces, pork bore a correlation
of 0.60 (p<0.01) with death from liver cirrhosis, while alcohol, perhaps due to
an overall low intake, showed no significant link.
And in statistical models incorporating known perils for the liver (alcohol consumption, hepatitis B infection and hepatitis C infection), pork remained independently associated with liver disease, suggesting the association isn't just due to pork piggybacking, as the case may be, on a different causative agent
Beef, by contrast, remained liver-neutral or protective in these studies.
Liver cancer, too, tends to follow in the hoof steps of the pig. A 1985 analysis showed that pork intake correlated with hepatocellular carcinoma deaths as strongly as alcohol did (0.40, p<0.05 for both) (49). (Considering liver cirrhosis is often a prelude to cancer, this connection shouldn’t be surprising
So, what's behind these eerie associations?
At first glance, the most likely explanations don't pan out. Although pork-transmitted hepatitis E can lead to liver cirrhosis, this happens almost exclusively in immunosuppressed people, a subset of the population that's too small to account for the global correlation
Relative to other meat, pork tends to be high in omega-6 fatty acids, including
linoleic acid and arachidonic acid, which may play a role in liver disease (.
But vegetable oils, whose polyunsaturated fatty acid content blows pork out of
the water, don't dance the same liver disease tango that pork does, calling into
question whether fat is really to blame
.
Heterocyclic amines, a class of carcinogens formed by cooking meat (including
pork) at high temperatures, contribute to liver cancer in a variety of animals (.
But these compounds are also readily formed in beef, according to the same
studies that indicated pork has no positive relationship with liver disease ().
With all that in mind, it'd be easy to dismiss the pork-liver disease link as an
epidemiological fluke. However, some plausible mechanisms do exist.
The most likely contender involves nitrosamines, which are carcinogenic
compounds created when
nitrites and nitrates
react with certain amines (from protein), particularly in high heat ). These
compounds have been linked to damage and cancer in a variety of organs,
including the liver .
One of the biggest dietary sources of nitrosamines is processed pork, which,
along with being a frequent visitor to the frying pan, typically contains
nitrites and nitrates as curing agents. (Vegetables are also rich in naturally
occurring nitrates, but their antioxidant content and dearth of protein help
thwart the process of N-nitrosation, preventing them from becoming
cancer-causing agents
.
Significant levels of nitrosamines have been found in pork liver pâté, bacon,
sausage, ham and other cured meats
. The fatty portion of pork products, in particular, tends to accumulate much
higher levels of nitrosamines than the lean bits, making bacon a particularly
abundant source (.
The presence of fat can also turn vitamin C into a nitrosamine promoter instead
of a nitrosamine inhibitor, so pairing pork with veggies might not confer much
protection ().
Although much of the nitrosamine-liver cancer research has focused on rodents,
where certain nitrosamines produce liver injury with remarkable ease, the effect
appears in humans as well
). In fact, some researchers suggest humans may be even more sensitive to
nitrosamines than mice and rats.
In Thailand, for instance, nitrosamines have been strongly linked to liver
cancer in areas where other risk factors are low
. A 2010 analysis of the NIH-AARP cohort found red meat (including pork),
processed meat
(including processed pork), nitrates and nitrites to be positively associated
with chronic liver disease. Rubber workers, occupationally exposed to
nitrosamines, have faced extremely high rates of non-alcohol-related liver
disease and cancer (72).
Do nitrosamines prove a chain of causation between pork, liver-harming compounds
and liver disease? The evidence is currently too patchy to make that claim, but
the risk is plausible enough to justify limiting nitrosamine-containing (or
nitrosamine-producing) pork products, including bacon, ham, hot dogs and
sausages made with sodium nitrite or potassium nitrate.
Summary:
Strong epidemiological links exist between pork consumption and liver disease.
If these links reflect cause and effect, one culprit might be
N-nitroso
compounds, which are found abundantly in processed pork products cooked at high
temperatures.
For years, pork's precautionary motto was "well-done or bust," a consequence of
fears about trichinosis, a type of roundworm infection that ravaged pork
consumers throughout much of the 20th
century
.
Thanks to changes in feeding practices, farm hygiene and quality control,
pig-borne trichinosis has dropped off the radar, inviting pink pork back onto
the menu.
But pork's relaxed heat rules may have opened the doors for a different type of
infection — yersiniosis, which is caused by Yersinia bacteria. In the US
alone, Yersinia causes 35 deaths and almost 117,000 cases of food
poisoning each year
). Its chief entry route for humans? Undercooked pork.
Yersiniosis's acute symptoms are rough enough — fever, pain, bloody diarrhea — but its long-term consequences are what should really ring alarm bells. Victims of Yersinia poisoning face a 47-times higher risk of reactive arthritis, a type of inflammatory joint disease triggered by infection
Even children become post-Yersinia arthritis targets, sometimes requiring chemical synovectomy (the injection of osmic acid into a troubled joint) to relieve persistent pain
And in the less-common instances where Yersinia doesn't bring the typical feverish, diarrheic unpleasantries? Reactive arthritis can develop even when the original infection was asymptomatic, leaving some victims unaware that their arthritis is a consequence of food-borne illness (
Although reactive arthritis usually subsides on its own over time, Yersinia
victims remain at higher risk of chronic joint problems, including ankylosing
spondylitis, sacroiliitis, tenosynovitis and rheumatoid arthritis, for years on
end
).
Some evidence suggests that Yersinia can lead to neurological complications (82). Infected individuals with iron overload may be at higher risk of multiple liver abscesses, potentially leading to death ). And among people who are genetically susceptible, anterior uveitis, inflammation of the eye's iris, is also more likely following a bout of Yersinia
Lastly, via molecular mimicry, Yersinia infection could also raise the
risk of Graves' disease, an autoimmune condition characterized by excessive
thyroid hormone production
).
The solution? Bring on the heat. The majority of pork products (69% of
tested samples, according to a
Consumer Reports analysis)
are contaminated with Yersinia bacteria, and the only way to safeguard
against infection is through
proper cooking.
An internal temperature of at least 145°F for whole pork and 160°F for ground
pork is necessary to decimate any lingering pathogen.
Summary:
Undercooked pork can transmit
Yersinia
bacteria, causing short-term illness and raising the risk of reactive arthritis,
chronic joint conditions, Graves’ disease and other complications.
So, should health-savvy omnivores scrap pork from the menu?
The jury's still out. For two of pork's problems — hepatitis E and Yersinia
— aggressive cooking and safe handling are enough to minimize the risk. And due
to a shortage of controlled, pork-centric research capable of establishing
causation, pork's other red flags spring from epidemiology — a field rife with
confounders and unjustified confidence.
Worse, many diet-and-disease studies lump pork together with other types of red
meat, diluting whatever associations might exist with pork alone.
These issues make it hard to isolate the health effects of pig-derived products
and determine the safety of their consumption.
That being said, caution is probably warranted. The sheer magnitude, consistency
and mechanistic plausibility of pork's connection with several serious diseases
make the chances of a true risk more likely.
Until further research is available, you might want to think twice about going
hog-wild on pork.
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