Ginkgo can’t prevent Alzheimer’s: large study
| | |
November 19, 2008
Filed under Uncategorized
AP, Globe and Mail, CTV — Ginkgo biloba, the herbal supplement that is sold in health-food stores as a memory enhancer, does not prevent the onset of dementia or Alzheimer’s disease, new research suggests.
The study is the largest and longest ginkgo biloba trial performed to date.
The dietary supplement ginkgo, long promoted as an aid to memory, didn’t help prevent dementia and Alzheimer’s disease in the longest and largest test of the extract in older Americans. “We don’t think it has a future as a powerful anti-dementia drug,” said Dr. Steven DeKosky of the University of Virginia School of Medicine, who led the federally funded study.
A note on dementia: Dementia refers to progressive symptoms such as memory loss, mood changes and a decline in the ability to talk, read and write caused by damage or changes to the brain. After Alzheimer’s disease, the most common cause of dementia is stroke. This type is referred to as vascular dementia.
Alzheimer’s disease affects about 300,000 Canadians over the age of 65, according to the Alzheimer’s Society of Canada. It is the most common form of dementia, has no cure, and is a progressive, degenerative disease that destroys brain cells.
Extracts from ginkgo tree leaves have antioxidant and anti-inflammatory effects, but earlier research on ginkgo and memory showed mixed results. Annual U.S. sales of the supplement reached $107 million in 2007, according to Nutrition Business Journal estimates.
For the new study, appearing in Wednesday’s Journal of the American Medical Association, researchers recruited more than 3,000 people, ages 75 and older, from voter and mailing lists in Maryland, Pennsylvania, California and North Carolina.
Half were randomly assigned to take 120 milligrams of ginkgo biloba twice a day, a typical dose taken by people who think it may help memory. The others took identical dummy pills.
Participants were screened for dementia every six months. After six years, dementia had been diagnosed at a similar rate in both groups; 277 in the ginkgo group and 246 in the group taking the dummy tablets. When the researchers looked only at Alzheimer’s disease, that rate too was similar.
The findings showed:
- 3.3 dementia cases per 100 persons per year in the Ginkgo biloba group compared to 2.9 cases among the placebo group.
- 3.0 Alzheimer’s cases per 100 persons per year in the Ginkgo biloba group compared to 2.6 among the placebo group.
At the start, some people showed mild difficulties with thinking; ginkgo didn’t work to prevent dementia in those people either.
Ginkgo appears relatively safe, DeKosky said. There was no difference in the rate of adverse events such as heart attacks and gastrointestinal bleeding between the groups. There were 16 strokes from bleeding in the brain in the ginkgo group versus eight in the placebo group, a difference that wasn’t statistically significant, he said, because the number of strokes was too small.
People on the blood thinner warfarin shouldn’t take ginkgo because of the risk of increased bleeding.
Proponents claim ginkgo protects the brain by preventing the buildup of an Alzheimer’s-related protein or by preventing cell-damaging oxidative stress.
Would ginkgo work better to prevent dementia if people started taking it earlier, say, in middle age? The study didn’t look at that, DeKosky acknowledged, adding that following people for 25 years from middle age to old age would be expensive research. The study also didn’t test whether ginkgo improves thinking and memory in the short term.
“It would have been terrific if this worked. It’s inexpensive, available and relatively safe,” said Paul Solomon, professor of neuroscience at Williams College in Williamstown, Mass., who wasn’t involved in the new study but has studied ginkgo.
“Now with this kind of evidence, you can confidently tell people it didn’t show benefit in more than 3,000 people in six years of research,” Solomon said.
There may still be a role for ginkgo in treating, rather than preventing, Alzheimer’s disease, said Michael McGuffin, president of the American Herbal Products Association, a trade association.
Some previous ginkgo trials have shown no benefit in Alzheimer’s symptom treatment, while others have found it comparable to prescription drugs such as Aricept, also known as donepezil.
The dementia study was funded by a grant from the National Institutes of Health’s National Centrr for Complementary and Alternative Medicine, which is undertaking large, scientific tests of a number of commonly used dietary supplements. The agency said it’s the largest-ever randomized trial of a botanical medicine. There have been larger studies of vitamins and minerals.
Side Effects and Cautions (From NCCAM)
- Side effects of ginkgo may include headache, nausea, gastrointestinal upset, diarrhea, dizziness, or allergic skin reactions. More severe allergic reactions have occasionally been reported.
- There are some data to suggest that ginkgo can increase bleeding risk, so people who take anticoagulant drugs, have bleeding disorders, or have scheduled surgery or dental procedures should use caution and talk to a health care provider if using ginkgo.
- Uncooked ginkgo seeds contain a chemical known as ginkgotoxin, which can cause seizures. Consuming large quantities of seeds over time can cause death. Ginkgo leaf and ginkgo leaf extracts appear to contain little ginkgotoxin.
The following strategies can help keep your heart and blood vessels healthy – and may also preserve your memory as you age (from Globe and Mail).
Reduce saturated and trans fats
Research has linked higher intakes of saturated (animal) fat with a two- to threefold greater risk of Alzheimer’s disease. Trans fats, found in many commercial baked goods and fried fast foods, have also been associated with an increased risk.
Choose lean cuts of meat, poultry breast and low-fat dairy products (1 per cent milk fat or less). Prepare foods with unsaturated fats such as olive oil, canola oil, flaxseed oil or non-hydrogenated margarine. Eat avocado and almonds; both are good sources of heart-healthy monounsaturated fat.
Eat more fish
Several studies have reported a lower risk of Alzheimer’s disease and cognitive decline among older adults who eat fish at least twice a week. Oily fish such as salmon, trout, sardines and herring are excellent sources of DHA (docosohexanoic acid), an omega-3 fatty acid that helps keep the lining of brain cells flexible so memory messages can pass easily between cells. Omega-3 fats also have anti-inflammatory effects in the brain.
The ideal intake of DHA for brain health is not known, but experts suggest a daily intake of 500 milligrams of DHA and EPA (eicosapentanoic acid) combined for heart health – an amount that can be obtained by eating three ounces of salmon twice a week. If you don’t like fish, consider taking a fish-oil capsule.
A six-year study of 3,718 people aged 65 and older reported that those who ate at least two to four servings of vegetables a day – versus less than one – had a significantly slower rate of cognitive decline.
Research suggests that leafy green vegetables such as spinach, kale, Swiss chard and rapini offer the greatest protection, probably because of their vitamin E content. (Vitamin E in foods is thought to protect brain cells from inflammation and free-radical damage.) While studies in humans have not found a link between fruit and cognitive decline, research in mice suggests blueberries can preserve memory.
Phytochemicals called anthocyanins, plentiful in blueberries and cranberries, are thought to combat free radicals.
Boost B-vitamin foods
An adequate intake of vitamin B12 and folate helps control blood levels of the amino acid homocysteine. Having a high homocysteine level is thought to damage artery walls and increase the risk of Alzheimer’s and other forms of dementia.
To get your B vitamins, eat a varied diet. Good sources of folate include lentils, cooked spinach, asparagus, avocados and oranges. Vitamin B12 is found in lean meat, fish, poultry, dairy products, eggs and enriched soy beverages. If you’re over 50, get your B12 from a multivitamin supplement, since absorption of the nutrient from foods decreases with age.
Physical activity is associated with slower mental decline. Exercise, especially aerobic activity, increases blood flow to the brain and could help maintain the health of brain cells.