L-肉鹼:好處、副作用、來源和劑量

L-carnitine is a naturally occurring amino acid derivative commonly taken as a supplement. It is used for weight loss and may have effects on brain function.

However, popular claims about supplements don't always line up with the science.

This article explores the potential risks and benefits of L- carnitine supplements and explains how this nutrient works in your body.

What is L- carnitine?

L- Carnitine is a nutrient and dietary supplement. It plays a vital role in energy production by transporting fatty acids into cellular mitochondria.

Mitochondria act as engines within the cell, burning these fats to produce usable energy. Your body can use lysine and methionine to create L- carnitine.

In order for your body to produce adequate amounts of vitamin C, you also need large amounts of vitamin C.

In addition to the L- carnitine produced in the body, you can also get small amounts of L- carnitine from consuming animal products such as meat or dairy products.

Vegetarians or people with certain genetic problems may not be able to produce or get enough food. This makes L- carnitine a conditionally essential nutrient.

Different types

L- Carnitine is the standard biologically active form of carnitine and is found in your body, food, and most supplements.

Here are several other types of carnitine:

  • D-Carnitine: This inactive form has been shown to reduce blood levels of carnitine and increase fat accumulation, leading to inflammation and oxidative stress in the liver.
  • Acetyl L- Carnitine: Commonly known as ALCAR, this is probably the most effective form for the brain. Research suggests it may benefit people with neurodegenerative diseases.
  • Propionil-L-Carnitine: This form is great for circulatory problems such as peripheral vascular disease and high blood pressure. According to some older research, it may boost nitric oxide production, which improves blood flow.
  • L- Carnitine L-Tartrate: Often added to sports supplements due to its rapid absorption. It may help with muscle soreness and recovery from exercise.

For most people, acetyl L- carnitine and L- carnitine appear to be the most effective for general use. However, you should always choose the format that best suits your personal needs and goals.

What it does in your body

L- Carnitine's primary effects in the body involve mitochondrial function and energy production.

In cells, it helps transport fatty acids into the mitochondria, where they can be burned for energy.

Over 95% of L- carnitine is stored in your muscles, with trace amounts found in your blood, liver, heart and kidneys.

L- carnitine may help enhance mitochondrial function, which plays a key role in disease and healthy aging.

The latest research illustrates the potential benefits of different forms of carnitine for treating a variety of conditions, including heart and brain disorders.

Does it help with weight loss?

Because L- carnitine helps move more fatty acids into cells to be burned for energy, it is sometimes used as a weight loss supplement.

A review of 37 studies found that L- carnitine supplementation significantly reduced body weight, body mass index (BMI), and fat mass. However, it had no effect on belly fat or body fat percentage.

Another analysis of nine studies, mostly in obese or older people, found that people who took L- carnitine lost an average of 2.9 pounds (lbs), or 1.3 kilograms (kg).

Additionally, a meta-analysis of six studies showed that L- carnitine can reduce body weight, body mass index, and abdominal fat in patients with PCOS.

Still, more research is needed to understand how it affects long-term weight loss.

Additionally, while it may help some people lose weight, you may want to consult a nutritionist first to develop a comprehensive diet and exercise regimen.

Effects on brain function

L- carnitine may benefit brain function.

Some research suggests that the acetyl form of acetyl L- carnitine (ALCAR) may help prevent age-related mental decline and improve learning abilities.

In fact, taking 1,500 milligrams (mg) of ALCAR daily for 28 weeks significantly improved brain function in people with dementia, according to a 2018 study.

However, other studies have produced mixed results.

For example, a 2017 review of two studies showed that taking L- carnitine for three days had no effect on measures of brain function, including reaction time, alertness, immediate memory, and delayed recall, in young adults without cognitive impairment.

Therefore, more research is needed on the potential benefits of supplements.

Other health benefits

L- carnitine supplements also have several other health benefits.

heart health

Some studies show that L- carnitine can benefit multiple aspects of heart health.

For example, a review of 10 studies found that L- carnitine significantly reduced diastolic blood pressure, especially in overweight and obese people.

Another analysis of 17 studies showed that L- carnitine can improve heart function and reduce symptoms in people with congestive heart failure.

Additionally, a 2020 review showed that L-carnitine can reduce total and LDL (bad) cholesterol while increasing HDL (good) cholesterol in people at risk for heart disease.

sports performance

Evidence is mixed regarding the effects of L-carnitine on exercise performance, but it may provide some benefits.

Keep in mind that the benefits of L-carnitine may be indirect and take weeks or months to appear. This is different from supplements like caffeine or creatine, which directly improve athletic performance.

L-carnitine may be beneficial in:

  • Recovery: It improves exercise recovery.
  • Muscle oxygen supply: It increases the oxygen supply to muscles.
  • Endurance: It may increase blood flow and nitric oxide production, helping to delay discomfort and reduce fatigue.
  • Muscle Soreness: It reduces muscle soreness after exercise.
  • Red blood cell production: It may increase the production of red blood cells, which carry oxygen throughout the body and muscles .
  • Performance: Take 60-90 minutes before exercise to improve high-intensity exercise performance.

type 2 diabetes

L-carnitine may be beneficial for people with type 2 diabetes.

A recent review of 41 studies concluded that L-carnitine supplementation can reduce fasting blood sugar and hemoglobin A1c (a marker of long-term blood sugar levels) while also improving insulin sensitivity in people with diabetes, overweight, or obesity.

According to the review's authors, L-carnitine is thought to work by altering insulin receptors and altering the expression of specific genes that regulate sugar metabolism .

It may also help improve the function of beta cells, the cells in the pancreas responsible for producing insulin .

frustrated

Some studies suggest L-carnitine may be beneficial in treating depression.

In a review of 12 studies, acetyl L-carnitine significantly reduced depressive symptoms compared with placebo.

Interestingly, several studies included in this review also found acetyl L-carnitine to be as effective as antidepressant medications but with fewer side effects.

Still, more research is needed to understand how L-carnitine affects depression.

Safety and side effects

For most people, taking 2 grams (g) or less per day is relatively safe and does not have any serious side effects.

Some studies have also used doses as high as 4,500 mg per day.

In a review of the safety of L-carnitine, doses of about 2 grams per day appeared to be safe for long-term use. However, there are some mild side effects, including heartburn and indigestion.

However, over time, L-carnitine supplements may increase blood levels of trimethylamine-N-oxide (TMAO). High levels of TMAO are associated with an increased risk of atherosclerosis, a disease that blocks arteries.

More research is needed on the safety of L-carnitine supplements.

food source

You can get small amounts of L-carnitine in your diet by eating meat and dairy products.

The best sources of L-carnitine are:

  • Beef: 139–143 mg per 3.5 ounces (oz) or 100 g
  • Pork: 25–61 mg per 3.5 oz (100 g)
  • Chicken: 13–34 mg per 3.5 oz (100 g)
  • Milk: 40 mg per 3.5 oz (100 g)
  • Hard cheese: 3 mg per 3.5 oz (100 g)

Interestingly, food sources of L-carnitine are better absorbed than supplements.

According to an earlier study, 57-84% of L-carnitine is absorbed when taken from food, compared with only 14-18% when taken as a supplement.

As mentioned earlier, your body can also produce this naturally from the amino acids methionine and lysine if your stores are low.

For these reasons, L-carnitine supplements are only needed in special circumstances, such as disease treatment.

Should you eat it?

Your L-carnitine levels are affected by how much you eat and how much your body produces.

Therefore, vegetarians and vegans often have lower L-carnitine levels because they limit or avoid animal products.

Therefore, vegetarians and vegans may want to consider L-carnitine supplements, which can help normalize carnitine levels in the blood and muscles.

Older adults may also benefit from L-carnitine supplements.

In fact, one study found that taking 1.5 grams of L-carnitine daily for 10 weeks improved functional status and frailty in older adults.

On the other hand, another study showed that L-carnitine supplementation had no effect on muscle strength or inflammation markers in older women.

The risk of vitamin D deficiency is also higher for people with conditions such as cirrhosis and kidney disease. If you have one of these conditions, supplements may help.

However, as with any supplement, you should consult your doctor before taking L-carnitine.

Dosage recommendations

Research on the potential benefits of L-carnitine has used a variety of doses.

Although dosage varies from study to study, here is an overview of the uses and dosage of each form:

  • Acetyl L-Carnitine: This form is best for brain health and function. The dosage range is 500–3,000 mg per day.
  • L-Carnitine L-Tartrate: This form is most effective for athletic performance. The dosage range is 1,000–4,000 mg per day.
  • Propionil L-Carnitine: This form may help improve blood flow in people with high blood pressure or related health conditions. One study used a dose of 2 grams per day.

generalize

Although more research is needed, L-carnitine may help promote weight loss and fat burning.

Research also supports its use in health, brain function, and disease prevention. Supplements may also benefit people with lower levels, such as older adults, vegetarians, and vegans.

Of the different forms, acetyl-L-carnitine and L-carnitine are the most popular and appear to be the most effective.

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