Much of the research on omega-3 fatty acids, found in oily fish, has focused on their benefits for the heart and mental health.
But the new study on mice, published in The Journal of Nutritional Biochemistry , adds to mounting evidence of their role in bone health.
The findings, still to be confirmed in humans, could offer an important prevention strategy for osteoporosis, currently second only to cardiovascular disease in terms of global healthcare burden, according to the World Health Organisation.
The condition affects some 200 million people today but the number of sufferers is set to increase steadily with growing numbers of elderly living longer, and obesity adding extra strain on bones.
"Age-related loss of bone mass and bone fragility are major risk factors for osteoporosis, leading to an increased risk of fractures," explained the authors.
"Therefore, nutritional strategies and lifestyle changes that prevent age-related osteoporosis and improve the quality of life for the elderly population are urgently needed."
Arunabh Bhattacharyaa and co-workers from the University of Texas Health Science Center at San Antonio, divided 12 month old C57BL/6 female mice into two dietary groups and supplemented AIN-93M semipurified diets with either omega-3 fatty acid-rich fish oil (10 per cent) or omega-6 fatty acid-rich corn oil (10 per cent).
After six months of dietary intervention, Bhattacharyaa and co-workers report that the fish oil-supplemented mice maintained higher BMD in different bone regions compared to the corn oil-fed mice.
In the fish oil-supplemented mice, bone mineral density increased significantly in distal femoral metaphysis (DFM) by 20 per cent, proximal tibial metaphysis (PTM) by 24 per cent and tibial diaphysis (TD) by 15 per cent, versus baseline.
In comparison, BMD increased only minimally in corn oil-fed mice.
BMD increased significantly in the femoral diaphysis (FD) bone region in mice groups, but the increase was higher in fish oil-supplemented mice compared to the corn oil-fed mice, 36 versus 25 per cent, respectively.
The beneficial findings amongst the fish oil-fed mice was also accompanied by a decreased activity of pro-inflammatory cytokines, tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), and lower osteoclast generation in bone marrow cell cultures.
Inflammation is caused by a number of compounds, including cytokines.
These compounds also stimulate bone breakdown, a natural part of a body process known as the bone cycle in which they are continuously broken down and rebuilt.
"Inhibition of pro-inflammatory cytokines and lower osteoclast generation suggest that higher BMD in FO-fed mice may be associated, in part, with both decreased bone resorption and higher bone formation," concluded the researchers.
"More studies with n-3 fatty acids and different ratios of n-6/n-3 fatty acids are warranted soon in middle-aged and older animals to establish their mechanism of action in modulating bone mass during aging."
While the new study results cannot yet be translated to humans, scientists have for some time been warning that the typical Western diet includes more omega-6 fatty acids than in the past, partly due to the reliance on high omega-6 grains like corn to feed livestock, which then alters the fats in the human diet.
The average American dietary ratio of omega-6 to omega-3 fatty acids is approximately 10 to 1. Source: The Journal of Nutritional Biochemistry (Elsevier) June 2007, Volume 18, Issue 6, Pages 372-379 "Effect of fish oil on bone mineral density in aging C57BL/6 female mice" Authors: A. Bhattacharyaa, M. Rahmana, D. Suna and G. Fernandes