There was a significant heterogeneity for the impact of CLA  on CRP and IL-6 , but not TNF-α .
Conclusions This meta- analysis showed that CLA supplementation may increase inflammatory markers ( CRP and TNF-α ) .
Background / objectives Conjugated linoleic acid ( CLA ) is a polyunsaturated fatty acid with attractive biological activities .
Numerous studies have been conducted on the inflammation-lowering effects of CLA in in vitro and animal models .
However , the effects of CLA treatment on the inflammatory markers in humans are controversial .
Effect of estrogen versus testosterone on circulating osteoprotegerin and other cytokine levels in normal elderly men.
Recent studies have shown that estrogen ( E ) likely plays a dominant role in inhibiting bone resorption in normal elderly men . Because both E and T inhibit osteoclast development and activity , stimulate osteoclast apoptosis , and inhibit osteoblast production of IL-6 , it is unclear why T is less potent than E in inhibiting bone resorption in vivo . Osteoprotegerin ( OPG ) binds to and inactivates RANKL , the final mediator of osteoclastogenesis . In vitro , OPG production is stimulated by E , and preliminary data suggest that T has the opposite effect . Thus , we analyzed serum for OPG levels from a study in which 59 elderly men ( mean age , 68 yr ) were made acutely hypogonadal using a GnRH agonist  and were also placed on an aromatase inhibitor to block conversion of and rogens to estrogens . They were studied first under conditions of physiologic E and T replacement , and then r and omized to no replacement , replacement with E alone , T alone , or both E and T. E alone result ed in an 18.6 + /- 7.9 % ( mean + /- SEM ) increase in serum OPG levels ( P < 0.05 ) , whereas T alone tended to decrease OPG levels ( by 10.0 + /- 8.5 % ; P < 0.05 compared with E alone ) . Using a two-factor ANOVA model , there was a highly significant T effect ( P = 0.006 ) on decreasing serum OPG levels . Serum TNF-alpha , IL-6 , and IL-6 soluble receptor levels increased significantly in the men who had both E and T withdrawn , and the increases in TNF-alpha and IL-6sR were absent in the men treated with either E or T. However , due to the variability in these cytokine measurements , the ANOVA models were not significant for E or T effects . Taken together , these data suggest that in vivo , T decreases OPG levels , whereas E tends to have the opposite effect . These differential effects of E vs. T on OPG production may explain , at least in part , why T has weaker effects than E on inhibiting bone resorption in vivo in humans
There was a significant heterogeneity for the impact of CLA  on CRP and IL-6 , but not TNF-α .
Conclusions This meta- analysis showed that CLA supplementation may increase inflammatory markers ( CRP and TNF-α ) .
Background / objectives Conjugated linoleic acid ( CLA ) is a polyunsaturated fatty acid with attractive biological activities .
Numerous studies have been conducted on the inflammation-lowering effects of CLA in in vitro and animal models .
However , the effects of CLA treatment on the inflammatory markers in humans are controversial .