膽固醇太低增加癌症和抑鬱症風險

http://renegadehealth.com/blog/2013/02/27/could-your-cholesterol-be-too-low-risks-include-cancer-and-depression
 

The Centers for Disease Control and Prevention (CDC) states that having high cholesterol puts you at risk of developing heart disease, the leading cause of death in the U.S. According to their statistics, 71 million American adults—over a third—have high LDL “bad” cholesterol, and people with high total cholesterol have twice the risk of heart disease as those with optimal levels.

Most of us already know this, and are getting regular blood tests to be sure our cholesterol doesn’t creep up too high. If it does, we have many options available to us, from an altered diet and lifestyle to medications.

While we’re all busy trying to lower our cholesterol levels, however, there’s another part of the conversation that’s missing—is it possible to have cholesterol levels that are too low? The answer is “yes,” particualrly for vulnerable populations like the elderly. In fact, for some people, cholesterol-lowering drugs are a very bad idea, as they can lead to increased mortality rather than extended life.

What is Cholesterol?

Cholesterol is a waxy, fat-like substance produced by the liver and found in animal-based foods. We make about 75 percent of the cholesterol in the blood, and get the other 25 percent from diet.

Cholesterol is vital for normal body function, and is used to make hormones, vitamin D, and other substances needed to digest foods. It also builds and maintains cell membranes, aids in the production of bile, insulates nerve fibers, and is important for the metabolism of fat-soluble vitamins.

Cholesterol is transporated through the body by three main lipoproteins. Lipoproteins contain both a lipid (fat like cholesterol) and a protein.

1. LDL “bad” cholesterol: Carries cholesterol from the liver out to the body cells. If too much goes out, this type of cholesterol can gather and buildup in the arteries, increasing the risk of artery narrowing and hardening.
2. HDL “good” cholesterol: Carries cholesterol away from cells and back to the liver. This is the cholesterol “clean up” lipoprotein.
3. Triglycerides: Triglycerides, in association with cholesterol, form blood fat. This fat is then used for energy when we need it, but if we don’t use it, it’s stored in fat cells.

What’s Considered an Optimal Cholesterol Level?

According to what we know so far from research, the following levels have been established:

Total Cholesterol

• Best: less than 200 mg/dL
• Borderline high: 200–239 mg/dL
• High: 240 mg/dL and above

LDL Cholesterol

• Best: Under 100 mg/dL
• Near Best: 100-129 mg/dL
• Borderline high: 130-159 mg/dL
• High: 160-189 mg/dL
• Very high: 190 mg/dL and above

HDL Cholesterol

• Best: 60 mg/dL and above
• Okay: 40-49 mg/dL (men), 50-59 mg/dL (women)
• Poor: Below 40 mg/dL (men), Below 50 mg/dL (women)

Triglycerides

• Best: Below 150 mg/dL
• Borderline high: 150-199 mg/dL
• High: 200-499 mg/dL
• Very high: 500 mg/dL and above

Look at these numbers and you’ll get the idea that your best bet for maintaining a healthy cardiovascular system is to get your cholesterol level (except for HDL) as low as possible.

According to some other studies, however, that could be dangerous.

Low Cholesterol Can Cause Early Death

In August 2001, the Honolulu Heart Program published a study in the journal the Lancet. Researchers studied 3,572 men who were 51 to 73 years of age at the start of the study. They took blood samples at the beginning, then again 20 years later (in 1991 and 1993), and deaths were determined over the next five years.

The results were suprising to a lot of people, because the greatest death rate was found in those whose cholesterol levels were the lowest at both the 1971 and 1991 examinations. Those with levels below 170 mg (considered optimal) had the highest death rates. Those over 210 mg had a significantly lower death rate than those with the lowest levels, but a bit higher than the group with the lowest death rate, which were those with levels of about 190 to 210 mg.

The researchers added, “the earlier patients started to have lower cholesterol concentrations, the greater the risk of death. These data cast doubt on the scientific justification for lowering cholesterol to very low concentrations (less than 180 mg) in elderly people.”

Other Studies Question Lowering Cholesterol Too Much

Though this was one of the largest studies questioning the wisdom of lowering cholesterol too much, there have been others.

• In 1994, Krumholz and colleagues published a study in JAMA. Results showed that elevated cholesterol was not a risk factor for mortality or heart disease in persons older than 70 years.
• A 1989 study in the Lancet found that women age 60 years and older with low cholesterol levels were at an increased risk for mortality.
• A 1997 study in the Lancet noted that “the impact of total serum cholesterol as a risk factor for cardiovascular disease decreases with age, which casts doubt on the necessity for cholesterol-lowering therapy in the elderly.” Researchers concluded that in people over 85 years, high total cholesterol is associated with longevity. They also noted that those participants with the highest cholesterol levels had a lower risk of cancer and infection.
• A 2004 study in the Journal of Women’s Health found that optimal cholesterol levels may vary depending on age and gender. Results showed that in men across the entire age range, although of borderline significance under the age of 50, and in women from the age of 50 onward only, low cholesterol was significantly associated with all-cause mortality—an increased risk of death through cancer, liver diseases, and mental diseases.

Risks of Low Cholesterol

What happens when cholesterol is too low? According to the Mayo Clinic, low levels of LDL cholesterol may increase your risk of cancer, depression, anxiety, and preterm birth and low birth weight. A study published in the Netherlands showed that middle-aged men with low cholesterol were more likely to experience severe depression, while an earlier study at the Duke University Medical Center showed that young women with levels below 160 mg were more likely to have depression and anxiety than women with normal or high cholesterol.

Recent studies from Germany linked low cholesterol with increased risk of agression, impulsivity, depression, and suicide. Other research shows that extra low levels can increase risk of Parkinson’s disease, stroke caused by bleeding in the brain, infertility and decreased libido, osteoporosis, hyperthyroidism, chronic indigestion, and nutrient deficiencies of fat-soluble vitamins.

Who May Have Low Cholesterol?

Though everyone is best advised to have their blood tested, the following can increase risk for low cholesterol levels:

• Marathons and other endurance sports
• Eating disorders
• Liver disease
• Hyperthyroidism
• Chronic stress
• Malnutrition or malabsorption
• High-sugar, low-fat diets

Best Approach Moving Forward?

Though we have some studies indicating that cholesterol may be protective against certain diseases, we have many more indicating that high cholesterol is associated with heart disease. Until science figures it all out, what’s the best approach for your optimal health?

Though there are no easy answers, moderation may be the key. If your cholesterol is particularly high, you may want to make lifestyle and diet changes to get it under control, but at the same time, be conscious that “lower is not always better.”

Studies so far seem to indicate that total cholesterol between 180 and 230 may be most protective. Lower than that may be dangerous. Higher than that? Consider other factors, such as your lifestyle, how active you are, and your cholesterol ratio—total to HDL should be at or below 5:1, according to the American Heart Association. Ideal at this time is considered 3.5 to 1. Adopting healthy habits is always a good idea, but drugs can come with serious side effects.

What’s a good level for one person may not be the best for another, as well. If you’re genetically predisposed to high cholesterol levels, you may need to adjust what’s “optimal” for you, as that may be a higher level than might be best for some other people. On the other hand, if you’re suffering from depression, anxiety, sexual dysfunctions, or other issues, you may want to talk to your doctor about whether your cholesterol levels may be too low.

Another thing to consider—your liver plays a key role in maintaining healthy cholesterol levels. If you’re struggling with high cholesterol, think about improving your liver function. Watch your diet, drink more water, and eat foods to support liver function.

Have you faced struggles with your cholesterol levels? Please share your story.

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Sources
“Cholesterol Facts,” Centers for Disease Control and Prevention, http://www.cdc.gov/cholesterol/facts.htm.

“What is Cholesterol? What Causes High Cholesterol?” Medical News Today, May 29, 2009, http://www.medicalnewstoday.com/articles/9152.php.

Mayo Clinic Staff, “Cholesterol levels: What numbers should you aim for?,” Mayo Clinic, September 21, 2012, http://www.mayoclinic.com/health/cholesterol-levels/CL00001.

Schatz IJ, et al., “Cholesterol and all-cause mortality in elderly people from the Honolulu Heart Program: a cohort study,” Lancet, 2001 Aug 4;358(9279): 351-5, http://www.ncbi.nlm.nih.gov/pubmed/11502313.

“Cholesterol Levels and Deaths: A Bit of a Shocker,” University of Medicine and Dentistry of New Jersey, August 2002, http://njms2.umdnj.edu/hwmedweb/archives/CholMortality_archive.htm.

Krumholz HM, et al., “Lack of association between cholesterol and coronary heart disease mortality and morbidity and all-cause mortality in persons older than 70 years,” JAMA 1994 Nov 2;272(17): 1335-40, http://www.ncbi.nlm.nih.gov/pubmed/7772105.

Forette B, et al., “Cholesterol as risk factor for mortality in elderly women,” Lancet, 1989 Apr 22;1(8643): 868-70, http://www.ncbi.nlm.nih.gov/pubmed/2564950.

Weverline-Rinjsburger AW, et al., “Total cholesterol and risk of mortality in the oldest old,” Lancet, 1997 Oct 18;350(9085):1119-23, http://www.ncbi.nlm.nih.gov/pubmed/9343498?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=3.

Ulmer H, et al., “Why Even is Not Adam: prospective follow-up in 149650 women and men of cholesterol and other risk factors related to cardiovascular and all-cause mortality,” J Womens Health (Larchmt), 2004 Jan-Feb; 13(1):41-53, http://www.ncbi.nlm.nih.gov/pubmed/15006277?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=10.

“Cholesterol: Can it Go Too Low?”, Dr. Weil, March 14, 2002, http://www.drweil.com/drw/u/id/QAA43423.