Effect of energy restriction and exercise on vitamin B-6 status of women during lactation

Purpose: Lactation increases vitamin B-6 requirements because its concentra tion in breast milk is related to maternal intake and it is essential for i nfants. Exercise may also increase the requirement because it increases uti lization and excretion of vitamin B-6. Therefore, the purpose of this study was to determine whether energy restriction and exercise affected vitamin B-6 status of lactating women. Methods: Breastfeeding women with a body mas s index greater than or equal to 25 and less than or equal to 30 kg.m(-2) w ere randomly assigned at 4 wk postpartum to either restrict energy intake b y 500 kcal.d(-1) and exercise for 45 min.d(-1), 4 d.wk(-1) (weight loss gro up, WG) or maintain usual diet and not exercise (control group, CG) for 10 wk. Women were given a supplement containing 2.0 mg of vitamin Ba. Measurem ents included vitamin B-6 concentrations in breast milk and plasma, plasma pyridoxal 5'-phosphate, and erythrocyte alanine aminotransferase activity. Results: The WG lost more weight (-4.4 +/- 0.4 vs -0.9 +/- 0.5 kg, P < 0.01 ) than the CG. Cardiovascular fitness increased by 12% in the WG, compared to 3% in the CG (P = 0.09). Milk vitamin B-6 concentrations increased in bo th groups (161 <plus/minus> 107 and 191 +/- 85 nmol.L-1, WG and CG, respect ively, P = 0.05). There were no significant differences in other vitamin B- 6 parameters. Weight and length gain (2.06 +/- 0.21 and 1.83 +/- 0.17 kg; 8 .6 +/- 0.6 and 7.2 +/- 0.5 cm; WG and CG, respectively) of infants was not significantly different between groups. Conclusions: Energy restriction and exercise from 4 to 14 wk postpartum in overweight, breastfeeding women con suming adequate dietary intakes and 2.0 mg of supplemental vitamin B-6 does not adversely affect vitamin Ba status or infant growth.