Fish/Fish Oil: Bone Health Benefits

Higher omega-3 fatty acids in blood = reduced risk of hip fractures

Higher levels of omega-3 fatty acids in the blood may reduce the risk for hip fractures in postmenopausal women, recent research suggests.

Scientists analyzed red blood cell samples from women with and without a history of having a broken hip. The study showed that higher levels of omega-3 fatty acids from both plant and fish sources in those blood cells were associated with a lower likelihood of having fractured a hip.

In addition to omega-3s, the researchers looked at omega-6 fatty acids, which are generally plentiful in a Western diet. The study also showed that as the ratio of omega-6 fatty acids to omega-3s increased, so did the risk for hip fracture.

Though the study did not define the mechanisms for these relationships, the researchers hypothesized that inflammation may contribute to bone resorption, the breaking down of bone caused by the release of cells called osteoclasts.

“Inflammation is associated with an increased risk of bone loss and fractures, and omega-3 fatty acids are believed to reduce inflammation. So we asked if we would see fractures decrease in response to omega-3 intake,” said Rebecca Jackson, the study’s senior author and a professor of endocrinology, diabetes and metabolism at The Ohio State University.

“One thing that was critically important was that we didn’t use self-report of food intake, because there can be errors with that. We looked directly at the exposure of the bone cell to the fatty acids, which is at the red blood cell level,” said Jackson, also associate dean for clinical research in Ohio State’s College of Medicine. “Red blood cell levels also give an indication of long-term exposure to these fatty acids, which we took into account in looking for a preventive effect.”

Broken hips are the most common osteoporosis-related fractures, with an estimated 350,000 occurring annually in the United States. About 20 percent of people die in the year following a hip fracture.

The research is published in a recent issue of the Journal of Bone and Mineral Research.

The observational study did not measure cause and effect, so the researchers say the findings are not definitive enough to suggest that taking omega-3 supplements would prevent hip fractures in postmenopausal women.

“We don’t yet know whether omega-3 supplementation would affect results for bone health or other outcomes,” said Tonya Orchard, assistant professor of human nutrition at Ohio State and first author of the study. “Though it’s premature to make a nutrition recommendation based on this work, I do think this study adds a little more strength to current recommendations to include more omega-3s in the diet in the form of fish, and suggests that plant sources of omega-3 may be just as important for preventing hip fractures in women.”

Omega-3 and omega-6 fatty acids are both polyunsaturated fatty acids and essential fatty acids, meaning they contribute to biological processes but must be consumed because the body does not produce them on its own. Previous research has suggested that while both types of fatty acids are linked to health benefits, omega-3 fatty acids have anti-inflammatory properties and omega-6 fatty acids seem to have both anti- and pro-inflammatory effects.

The researchers used blood samples and hip fracture records from the Women’s Health Initiative (WHI), a large national prospective study of postmenopausal women that enrolled participants between 1993 and 1998 and followed them for 15 years. For this new work, the sample consisted of red blood cell samples and records from 324 pairs of WHI participants, half of whom had broken their hips before Aug. 15, 2008, and the other half composed of age-matched controls who had never broken a hip.

The analysis showed that higher levels of total omega-3 fatty acids and two other specific kinds of omega-3s alone were associated with a lower risk of hip breaks in the study sample.

On the other hand, women who had the highest ratio of omega-6 to omega-3 fatty acids had nearly twice the risk of hip fractures compared to women with the lowest ratios. The current typical American diet contains between 15 and 17 times more omega-6 than omega-3, a ratio that previous research has suggested should be lowered to 4-to-1, or even 2-to-1, by increasing omega-3s, to improve overall health. The primary omega-6 fatty acid in the diet is linoleic acid, which composes about 99 percent of Americans’ omega-6 intake and is found in corn, soybean, safflower and sunflower oils.

The specific omega-3 sources associated with lower risk for broken hips were ALA (alpha-linolenic acid), which comes from plant sources such as flaxseed oil and some nuts, and EPA (eicosapentaenoic acid), which is found in fatty types of fish. The other marine-sourced omega-3, DHA (docosahexaenoic acid), on its own did not have a significant link to lower hip-fracture risk, “but all three omega-3s were in the protective direction,” Orchard said.

Jackson, who was a vice chair of the WHI for more than a decade, said continuing analyses of data from the WHI will dig down to the genetic influences on metabolism and absorption of nutrients, and whether such genetic differences could affect health risk factors in postmenopausal women.

Omega-3 May Help Reduce Bone Loss

NASA-sponsored studies have found that omega-3 fatty acids found in fish oil may play a role in mitigating bone breakdown that occurs during spaceflight and in osteoporosis. Ongoing research for decades has looked for ways to stop bone density loss in astronauts. The solution could have significant implications for space travelers and those susceptible to bone loss on Earth.

The studies' results are published in the May, 2010 issue of the Journal of Bone and Mineral Research. The paper reports on four types of studies using cell culture, ground-based bed rest, and data from both space shuttle and International Space Station crew members. NASA studies bone density loss because it is one of the main effects of exposure to the weightlessness of space. Scientists hope to find ways to counteract the problem for astronauts on long-duration space voyages.

In a series of cell-based studies, scientists documented that adding a specific omega-3 fatty acid to cells would inhibit the activation of factors that lead to bone breakdown. This was true in both typical cell cultures and those designed to mimic weightlessness. The inhibited factor is known as "nuclear factor kappa B" or NF_B. NF_B is involved in immune system behavior and the inflammation process. The activation of NF_B in different tissues can lead to bone and muscle loss.

In a study of astronauts returning from short-duration shuttle missions, researchers found that NF_B activation was increased in blood cells collected at landing, and remained elevated for two weeks. These data provide evidence that inflammatory processes may be involved in some of the adaptation to microgravity and suggest that reducing NF_B activation could serve as a countermeasure to bone loss.

A ground-based bed rest study was conducted on 16 subjects with the evaluations performed after 60 days. Bed rest simulates some of the effects of weightlessness, including muscle and bone loss. During the study, higher intake of omega-3 fatty acids was associated with less bone loss.

Based on these studies, the investigators evaluated bone loss in astronauts and compared their findings to reported fish intake during spaceflight. Researchers found that astronauts who ate more fish lost less bone mineral after four-to-six-month spaceflights. Tracking fish consumption is not as accurate as determining exact diet and omega-3 fatty acid intake, but these data were not available.

"These results are very exciting, and provide initial evidence that nutrition may be a key factor in mitigating bone loss in astronauts." said Scott Smith, a nutritionist at NASA's Johnson Space Center in Houston and one of the paper's authors.