The Effect of Different N-6/n-3 Essential Fatty Acid Ratios on Calcium Balance and Bone in Rats.
The Effect of Different N-6/n-3 Essential Fatty Acid Ratios on Calcium Balance and Bone in Rats.
Year: 1995
Authors: N Classen, H Coetzer, M L Steinmann, M C Kruger.
Publication Name: Prosta. Leukot. Essent. Fatty Acids.
Publication Details: Volume 53; Number 1; 13.
Abstract:
Prostaglandins (PGs) are known to have various effects on bone metabolism. PGs of the series 1 derived from GLA and of the series 3, derived from EPA, are involved in intestinal calcium absorption and calcium balance. However, controversy exists as to whether increased calcium absorption and calcium balance will enhance the calcium content in bone. The authors hypothesized that EFAs of the n-6 and n-3 families may need to be provided in a specific ratio to obtain optimum effects on calcium metabolism. The objective of this study was to investigate the effect of different ratios of n-6:n-3 PUFAs on calcium balance and bone mineralization. Forty male Sprague-Dawley rats aged 5-12 weeks were supplemented with the EFAs, LA and ALA, which were administered in a ratio of 3:1 as a control group. Fatty acids beyond the rate-limiting step of delta-6-desaturation, GLA and EPA, were administered to different groups of rats in ratios of 3:1, 1:1 and 1:3 to determine the effects of different ratios of n-6:n-3 PUFAs on calcium balance. After six weeks, the results showed that the plasma levels of GLA:EPA increased more than the actual amounts supplemented in the diet. Calcium excretion in the feces decreased of 27% in the 3:1 group and 20.3% in the 1:3 group in comparison to the control animals. Intestinal calcium absorption (mg/24 h) increased by 41.5% and 21.4% in the 3:1 and 1:3 supplemented groups, respectively, compared with a value of 48% in the control group. A decrease in urinary calcium (mg/24 h) was found which correlated with increasing dietary n-3 level. The calcium balance (mg/24 h) and bone calcium (mg/g bone ash) increased significantly in the 3:1 (41.5% and 24.7%) group, compared with the control group. Bone calcium levels were also significantly increased in the 1:1 supplemented group (9%). The results indicated a lack of response in urinary calcium in the 3:1 group which suggests that EPA levels should exceed a certain threshold above GLA before reductions in urinary calcium will occur. Increased EPA levels appear to be associated with reduced output of urinary calcium as a negative relationship was noted between dietary EPA and urinary calcium. Higher calcium absorption leading to improved calcium balance occurred in the 3:1 GLA:EPA group which indicates the importance of PGE1 in calcium metabolism. The authors speculated that the increase in bone calcium may be attributed to an EFA-induced increase in circulating PGs. The results of this study indicate that GLA and ALA/EPA in appropriate dietary ratios increases the synthesis of PGs acting on target bone cells and cause beneficial alterations in membrane fluidity. These effects appear to be beneficial in enhancing calcium balance and calcium content of bone.
