How does smoking affect the liver?

The liver's primary responsibility is removing toxins from the body. It does this by filtering the blood to separate substances that are good for the body from those that are toxic to the body. The more toxins that are filtered, the less efficient the liver is at performing this duty. Cigarette smoking induces certain cytochrome P450 enzymes[1] in the liver, causing them to accelerate their activity, thus breaking down chemicals at a faster rate. As a result, medications that are eliminated by those enzymes are also eliminated at a faster rate, decreasing their levels in the body and rendering them less effective. This may affect the dose of medication required to treat a particular disease. It is important to let your doctor know that you are smoking, as this may prompt her or him to alter the dose of a medication if it is not working.

Despite this observation, as yet there is no conclusive evidence that tobacco use has an adverse effect on the liver, although cigarettes may worsen the course of alcoholic liver disease. Additionally, other studies have suggested that tobacco smoking may promote the progression of fibrosis in hepatitis C patients, accelerating the disease process, although this has been less extensively studied than alcohol. The accelerated fibrosis associated with cigarette smoking may be triggered by lower oxygen levels on a microvascular level in smokers. Therefore, it is recommended that people with liver disease refrain from using these forms of tobacco as well.

Are there any health benefits to tobacco or nicotine?

Tobacco, when used for specific purposes has long been considered to be safe, if not healthy in its history. Native Americans understood and appreciated its toxicity when used excessively either in quantity or frequency. Limited to specific ceremonies and to the pharmacopeia of the Medicine Men and Women, tobacco was regarded as a perfectly acceptable healing herb. It was used as a pain killer for earache and toothache and occasionally as a poultice. It was used by the desert Indians to be a cure for colds, especially if mixed with the leaves of the small desert sage, or the root of Indian balsam or cough root, which was thought to be particularly good for asthma and tuberculosis. In addition it was often eaten to be used as a purgative or in enemas. In 1571, a Spanish doctor wrote a book about the history of medicinal plants of the New World, including tobacco, which was thought to cure 36 health problems. When tobacco first arrived in the Ottoman Empire, it attracted the attention of doctors and became a commonly prescribed medicine for many ailments. Until the first Surgeon General's Report in 1964, tobacco companies often enlisted the support of physicians to promote smoking. One can see 1950s TV commercials and magazine ads with physicians, glamorous movie and TV stars, and even athletes promoting its use.

While the idea of tobacco conferring any health benefits today seems almost ludicrous, the issue of nicotine's positive impact on health remains hotly investigated. A number of people with neuropsychiatric conditions tend to smoke heavily. These conditions include attention deficit hyperactivity disorder (ADHD), depression, and schizophrenia. All of these conditions share the symptom of inattention as an underlying problem. Nicotine, as a stimulant, impacts dopamine, a major neurotransmitter in the maintenance of attention. Studies using functional magnetic resonance imaging (fMRI) in smokers demonstrate that nicotine clearly improved the activity of areas of the brain known to be involved in attention. In addition, researchers have found genes regulating specific nicotine receptors in schizophrenics to be reduced. A recent study conducted by Robert Freedman, MD, at the University of Colorado and published in the June 2006 issue of Archives of Psychiatry, tested a drug that targets that specific nicotine receptor. In that small study, the drug, known as DMXB-A[2], was found to improve certain cognitive symptoms in schizophrenia. Paul Newhouse at the University of Vermont is investigating nicotine and nicotine-related drugs in ADHD.

Smokers appear to have lower rates of neurodegenerative disorders, such as Alzheimer's disease, Parkinson disease, multiple sclerosis, and Huntington chorea. This may be due to the fact that nicotine boosts the neurotransmitters dopamine and acetylcholine, which play roles in these conditions. Newhouse is also experimenting with using nicotine patches to treat mild cognitive impairment, a possible precursor to Alzheimer's disease.

Nicotine also plays a role in obesity and pain. Nicotine historically was used to treat toothache. In animals it has been demonstrated to provide modest pain relief. Recently, epibatidine, a drug extracted from a South American frog that acts on nicotine receptors, has been found to be 200 times more potent than morphine in blocking pain in animals. Other researchers have demonstrated that intranasal nicotine use reduces the need for morphine in some postoperative patients. Nicotine is also being investigated in weight control, a problem every ex-smoker struggles with soon after they quit. Nicotine appears to up-regulate certain hormones that play a role in appetite regulation so that appetite is suppressed by their increase. In one study on rats, the animals were able to lose not only their weight, but also 20% of their body fat. Nicotine appears to affect all molecules that are known to influence weight, which may be one of the earliest nicotine- based treatments that are nonsmoking related.

Before you jump to a nicotine replacement therapy to treat or "prevent" any of these conditions, it is important to remember that the research is ongoing and none of the benefits listed here are either well validated or risk-free. The risks of nicotine are well known, particularly when used in excess, and most notably include cardiorespiratory collapse and death, aside from the risks associated with any stimulant that is addictive.

  • [1] A group of enzymes found in the liver that function to break down chemicals for elimination from the body. These chemicals include but are not limited to medications. Some medications can block these enzymes while other medications or drugs, such as nicotine, can induce or accelerate these enzymes.
  • [2] A drug that activates the alpha-7 subtype of the nicotine receptor and is being used experimentally to improve cognition in patients with Alzheimer's disease and schizophrenia.
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