Vitamin D and long-chain omega-3s (EPA and DHA) are the essential nutrients in which fish – especially fatty fish – are uniquely rich.
Scientists suspect that dietary omega-3s reduce the risk of osteoporosis by reducing inflammation, decreasing activation of osteoclasts (cells that break down bone), and helping the body absorb calcium.
As Iranian researchers wrote three years ago, the evidence that omega-3s enhance bone health is encouraging, but needs more confirmation from human clinical trials:
“Generally, animal studies support the beneficial effects of omega-3 fatty acids on bone health and osteoporosis; however, the dissimilar lipid [fat] metabolism in human and animals, varying [human] study designs, and controversies over human study outcomes make it difficult to draw a definite conclusion.” (Salari P et al. 2008)
In the meantime, an analysis of health and diet data from the large Framingham Osteoporosis Study adds substantial epidemiological evidence in favor of omega-3s (Farina EK et al. 2011).
Just as important, it supports prior indications that Americans' grossly excessive intake of omega-6 fatty acids has bone-weakening effects.
And it was seen in findings from the University of California's Rancho Bernardo Study, conducted among 1,532 people aged 45 to 90.
As the UC San Diego team wrote six years ago, “A higher ratio of omega-6 to omega-3 fatty acids is associated with lower BMD [bone mineral density] at the hip in both sexes.” (Weiss LA et al. 2005)
Study supports value of omega-3s and risks of excess omega-6s
The new findings come from Tufts University researchers in Boston, who analyzed diet surveys and bone-health data from more than 600 volunteers in the Framingham Osteoporosis Study (Farina EK et al. 2011).
Their analysis found that older adults who reported consuming the most omega-3 fatty acids were more likely to have maintained adequate bone mineral density in their hips four years later.
The study's authors came to this conclusion after analyzing dietary surveys and bone scans from 623 adults enrolled in the Framingham Osteoporosis Study (average age 75).
Only the long-chain omega-3s in fish and fish oil (EPA and DHA) appear to have this effect.
In contrast, when omega-3 intakes are low, high intake of either the long-chain omega-6 fat in animal foods (AA) or the short-chain omega-6 in plants foods (LA) may weaken bones.
The current study found that, as a general principle, people who ate the most fish – three or more servings per week – were more likely to have healthy bone mineral levels in the hips, as measured by bone mass density scans of their upper femurs.
However, the team found distinctions when they looked at varying intakes of omega-3s and omega-6s in relation to each other:
Among men who consumed very little EPA and DHA, those who got the most AA from their diets lost more bone mass than those with the least dietary AA.
Among older women who consumed more than the average amount of omega-3 EPA and DHA, those who also consumed more than the average amount of omega-6 AA tended to have higher bone density in their hips.
Higher intake of omega-6 LA was linked to more bone loss in women, compared with lower intakes of LA.
In other words, omega-6 AA seems to promote bone loss when your diet is low in omega-3s.
In contrast, diets high in omega-3s from fish and omega-6 AA may confer a slight hip-bone advantage over diets high in omega-3s that contain less omega-6 AA.
The USDA-funded Tufts team concluded that frequently consuming fish may delay the onset of osteoporosis, and that AA's positive effects only appear when people are getting more omega-3s than the average American.
Farina EK, Kiel DP, Roubenoff R, Schaefer EJ, Cupples LA, Tucker KL. Protective effects of fish intake and interactive effects of long-chain polyunsaturated fatty acid intakes on hip bone mineral density in older adults: the Framingham Osteoporosis Study. Am J Clin Nutr. 2011 Mar 2. [Epub ahead of print]
Högström M, Nordström P, Nordström A. n-3 Fatty acids are positively associated with peak bone mineral density and bone accrual in healthy men: the NO2 Study. Am J Clin Nutr. 2007 Mar;85(3):803-7.
Orchard TS, Cauley JA, Frank GC, Neuhouser ML, Robinson JG, Snetselaar L, Tylavsky F, Wactawski-Wende J, Young AM, Lu B, Jackson RD. Fatty acid consumption and risk of fracture in the Women's Health Initiative. Am J Clin Nutr. 2010 Dec;92(6):1452-60. Epub 2010 Oct 27.
Salari P, Rezaie A, Larijani B, Abdollahi M. A systematic review of the impact of n-3 fatty acids in bone health and osteoporosis. Med Sci Monit. 2008 Mar;14(3):RA37-44. Review.
Weiss LA, Barrett-Connor E, von Mühlen D. Ratio of n-6 to n-3 fatty acids and bone mineral density in older adults: the Rancho Bernardo Study. Am J Clin Nutr. 2005 Apr;81(4):934-8.