Consumption of different sources of omega-3 polyunsaturated fatty acids by growing female rats affects long bone mass and microarchitecture.

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) consumption has been reported to improve bone health.  However, sources of ω-3 PUFAs differ in the type of fatty acids and structural form. The study objective was to determine the effect of various ω-3 PUFAs sources on bone during growth. Young (age 28 d) female Sprague Dawley rats were randomly assigned (n=10/group) to a high fat 12% (wt) diet consisting of either corn oil (CO) or ω-3 PUFA rich, flaxseed (FO), krill (KO), menhaden (MO), salmon (SO) or tuna (TO) for 8 weeks. Bone mass was assessed by dual-energy X-ray absorptiometry (DXA) and bone microarchitecture by microcomputed tomography (μCT). Bone turnover markers were measured by enzyme immunoassay. Lipid peroxidation was measured by calorimetric assays. Results showed that rats fed TO, rich in docosahexaenoic acid (DHA, 22:6 ω-3) had higher (P < 0.009) tibial bone mineral density (BMD) and bone mineral content (BMC) and lower (P=0.05) lipid peroxidation compared to the CO-fed rats. Reduced lipid peroxidation was associated with increased tibial BMD (r2=0.08, P=0.02) and BMC (r2=0.71, P=0.01). On the other hand, rats fed FO or MO, rich in alpha-linolenic acid (ALA, 18:3 ω-3), improved bone microarchitecture compared to rats fed CO or SO. Serum osteocalcin was higher ( P=0.03) in rats fed FO compared to rats fed SO. Serum osteocalcin was associated with improved trabecular bone micoarchitecture. The animal study results suggest consuming a variety of ω-3 PUFA sources to promote bone health during the growth stage. (Author's Abstract) 

Maximizing peak bone mass is considered a major factor in reducing the future risk of osteoporosis. Some studies have reported a bone protective effect of ω-3 PUFAs; whereas, others have reported no effect. These inconsistent findings may be due to different ω-3 PUFAs having different biological properties and physiological effects.  Gender differences may also influence the effects of ω-3 PUFAs on bone. Few rat studies have investigated the effects of feeding a diet rich in ω-3 PUFAs on bone development in female rats. ω-3 PUFAs may affect bone by altering calcium (Ca) balance, bone turnover, and inflammation influence bone turnover by altering osteoclastic and osteoblastic differentiation and activity. This study demonstrated that growing female rats fed a high (12% by weight) fat diet as ω-3 PUFAs have a positive effect on the long bones. Rats fed FO – high in ALA – had increased tibial trabecular bone microarchitecture indicated by significantly higher BV/TV compared to rats fed CO or SO. In the femur, rats fed FO or MO had higher BV/TV that was associated with a greater trabecular number and reduced trabecular separation compared to rats fed CO. The sources of ω-3 PUFA that improved bone microarchitecture quality were MO and particularly, FO. The results suggest that ALA improved long bone microarchitecture in growing female rats. No differences were detectable in bone strength among rats fed different sources of ω-3 PUFAs.  ALA promoted bone formation indicated by higher serum osteocalcin. In summary, the source of ω-3 PUFAs is an important factor in bone metabolism. Of the ω-3 PUFAs sources, only growing rats fed KO with the highest EPA and DHA in phospholipid form failed to improve bone mass or microarchitecture and reduced bone size. Growing female rats fed TO with the highest DHA or SO with the highest EPA content in the triglyceride form resulted in increased bone mass associated with lower lipid peroxidation. Rats fed FO or MO with the highest ALA content of the oil sources, resulted in improved bone microarchitecture associated with increased bone formation.  The results suggest that rather than focusing on one source of ω-3 PUFAs, perhaps a variety of ω-3 PUFA sources should be consumed in order to improve bone health during the growth stage. (Editor's comments)