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The Cochrane Library Newsalert: Omega-3 and Cognitive Decline; Blood Sugar Control in Diabetes; Weekly Fertility Injections
08 June 2012
This alert highlights some of the key health care conclusions and their implications for practice publishing next week in The Cochrane Library, 2012, Issue 6.
Reviews highlighted in this newsalert:
* Role of Omega-3 in Preventing Cognitive Decline in Older People Questioned
* Diabetes: Tighter Control of Blood Sugar Prevents Nerve Condition, But At What Risk?
* New Weekly Fertility Injections Work As Well As Daily
Role of Omega-3 in Preventing Cognitive Decline in Older People Questioned
Older people who take omega-3 fish oil supplements are probably not reducing their chances of losing cognitive function, according to a new Cochrane systematic review. Based on the available data from studies lasting up to 3.5 years, the researchers concluded that the supplements offered no benefits for cognitive health over placebo capsules or margarines, but that longer term effects are worth investigating.
Omega-3 fatty acids are fats responsible for many important jobs in the body. We get these fats through our daily diets and the three major omega-3 fats are: alpha linolenic acid (ALA) from sources such as nuts and seeds and eicosapentoic acid (EPA) and docosahexaenoic acid (DHA) from sources including oily fish such as salmon and mackerel. A number of studies have hinted that omega-3 fatty acids and DHA in particular may be involved in keeping nerve cells in the brain healthy into old age. However, there is limited evidence for the role of these fats in preventing cognitive decline and dementia.
The researchers, led by Emma Sydenham at the London School of Hygiene & Tropical Medicine (LSHTM), London, UK, gathered together evidence from three high quality trials comparing the effects of omega-3 fatty acids taken in capsules or margarine spread to those of sunflower oil, olive oil or regular margarine. A total of 3,536 people over the age of 60 took part in the trials, which lasted between six and 40 months. None of the participants had any signs of poor cognitive health or dementia at the start of the trials. The researchers found no benefit of taking the omega-3 capsules or spread over placebo capsules or spread. Participants given omega-3 did not score better in standard mental state examinations or in memory and verbal fluency tests than those given placebo.
“From these studies, there doesn’t appear to be any benefit for cognitive health for older people of taking omega-3 supplements,” said Alan Dangour, a nutritionist at LSHTM and co-author of the report. “However, these were relatively short-term studies, so we saw very little deterioration in cognitive function in either the intervention groups or the control groups. It may take much longer to see any effect of these supplements.”
The researchers conclude that the longer term effects of omega-3 fatty acids on cognitive decline and dementia need to be explored in further studies, particularly in people with low intakes of omega-3 fatty acids in their diet. In the meantime, they stress other potential health benefits. “Fish is an important part of a healthy diet and we would still support the recommendation to eat two portions a week, including one portion of oily fish,” said Dangour.
Diabetes: Tighter Control of Blood Sugar Prevents Nerve Condition, But At What Risk?
Aggressive control of blood sugar levels in diabetes can help to prevent a painful condition affecting patients’ nerves, according to a new systematic review in The Cochrane Library. However, the review suggests that optimal target levels need to be established to prevent serious complications.
People with diabetes control their blood sugar levels through insulin injections, diet and drugs, to compensate for their bodies producing too little insulin (type 1 diabetes) or becoming resistant to insulin (type 2 diabetes). Up to half of people with diabetes develop a disabling condition called diabetic neuropathy, which affects nerves in the feet and legs, making them feel tingly, numb, painful or weak. It is possible to prevent neuropathy by strict control of blood sugar levels through a number of ways including different insulin regimens and diet modification, but evidence for the effects of this approach, known as enhanced glucose control, has not been systematically reviewed until now.
The results analysed in the review are drawn from six studies investigating the risk of neuropathy in people who received enhanced glucose control treatments including extra insulin injections, antidiabetic drugs, and diet changes. The review looked at evidence in type 1 and type 2 diabetes separately. In two studies involving 1,228 people with type 1 diabetes significantly fewer people developed neuropathy each year with enhanced glucose control treatment compared with routine care. In four studies involving 6,669 people with type 2 diabetes the reduction in new cases of neuropathy was small and not statistically significant.
“Overall, this evidence suggests that a more aggressive approach to controlling sugar levels can be effective in delaying the onset of neuropathy in diabetes,” said lead author of the review, Brian Callaghan, M.D., Assistant Professor in the Department of Neurology at the University of Michigan in Ann Arbor, Michigan, US. “The results also highlight the differences between type 1 and type 2 diabetes. The less dramatic effect of enhanced glucose control in type 2 diabetes may indicate that other factors, besides high glucose levels, may be important in causing nerve damage in these patients.”
However, the risk of adverse effects associated with the treatment, including hypoglycaemia, was higher with enhanced glucose control. The researchers say further research is needed to optimise target levels for safe treatments that will both prevent neuropathy and minimise serious side effects.
“Although these results show clear benefits for preventing neuropathy in people with diabetes, they should be weighed against potential adverse effects,” said Callaghan. “Future studies must establish target levels for glucose control that will balance benefits and side effects.”
New Weekly Fertility Injections Work As Well As Daily
New long-lasting weekly injections of fertility hormones are as safe and effective as standard daily injections, according to Cochrane researchers. The researchers compared weekly and daily hormone injections in a Cochrane systematic review and found no difference in pregnancies or serious side effects between the two regimens.
Women undergoing fertility treatment are usually given daily injections of follicle stimulating hormone (FSH) to increase the number of eggs that their ovaries release each month. In in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI), the eggs are then removed and fertilised outside the body. Daily hormone injections can be painful and stressful but a new longer-lasting FSH, known as corifollitropin alfa, has recently been introduced. One injection of this longer-lasting hormone can replace the first seven days of FSH injections required in the standard treatment regimen.
The researchers included data from four trials involving 2,335 people in their review. They show that women given medium doses of the new long-lasting hormone on a weekly basis are equally likely to become pregnant and are no more likely to have a miscarriage or ectopic pregnancy than those receiving daily FSH injections.
“These results show that the new long-acting injections are a safe treatment option and equally effective in medium doses compared to the standard daily injections,” said Jan Kremer, one of the authors of the review based at the Radboud University Nijmegen Medical Center in Nijmegen, Netherlands.
However, there is currently limited information about patient satisfaction with long-lasting FSH. “One of the main reasons weekly injections are considered preferable to daily injections is that they are more patient friendly,” said Kremer. “So are couples undergoing fertility treatment happier with weekly injections? We would like to see research addressing this question.”
Further research is also needed to establish whether long-acting injections are as effective in women who respond poorly to fertility hormones and those who ‘hyperrespond’, meaning they produce higher than expected numbers of eggs.