Acute Folic Acid Ingestion Improves Skeletal Muscle Blood Flow during Graded Handgrip and Plantar Flexion Exercise in Aged Humans

Abstract

Skeletal muscle blood flow is attenuated in aged humans performing aerobic exercise, which is thought to be due, in part, to impaired local vasodilatory mechanisms. Recent evidence suggests that folic acid improves cutaneous vasodilation during localized and whole‐body heating through nitric oxide‐dependent mechanisms. However, it is unclear if folic acid can improve vasodilation in other vascular beds during conditions of increased metabolism (i.e. exercise). Therefore, the purpose of this study was to test the hypothesis that acute folic acid ingestion would improve skeletal muscle blood flow in aged adults during graded handgrip and plantar flexion exercise via increased vascular conductance. Eight healthy aged adults (2 males; age 68 ± 5 years; height 165 ± 6 cm; weight 70 ± 8 kg; mean ± SD) performed graded handgrip (3, 6, 9 kg) and plantar flexion (5, 9, and 14 kg) exercise before (control) and two hours after folic acid ingestion (5 mg). Exercise was performed using a duty cycle of 1 s contraction and 2 s relaxation (20 contractions min−1). Steady‐state forearm (brachial artery) and leg (superficial femoral artery) blood flow and diameter were measured via Duplex ultrasonography. Vascular conductance was calculated as flow/pressure and multiplied by 100. Blood flow and vascular conductance are presented as the mean response across exercise intensity. Acute folic acid ingestion increased serum folate (control 12.8 ± 1.7 ng ml−1 vs folic acid 493.3 ± 85.5 ng ml−1; P < 0.01). During handgrip exercise, folic acid ingestion increased forearm blood flow (control Δ 91 ± 7 ml min−1 vs folic acid Δ 113 ± 9 ml min−1; P < 0.01) and vascular conductance (control Δ 97 ± 7 ml min−1 100 mmHg−1 vs folic acid Δ 114 ± 8 ml min−1 100 mmHg−1; P < 0.01). Similarly, during plantar flexion exercise, folic acid ingestion increased leg blood flow (control Δ 226 ± 19 ml min−1 vs folic acid Δ 284 ± 21 ml min−1; P < 0.01) and vascular conductance (control Δ 244 ± 20 ml min−1 100 mmHg−1 vs folic acid Δ 281 ± 20 ml min−1 100 mmHg−1; P = 0.01). Taken together, acute folic acid ingestion improves blood flow to active skeletal muscle via improved local vasodilation in aged adults.Support or Funding InformationFunded by National Institutes of Health (GM 068865 & GM 117693).