Improvement in blood pressure after short-term inorganic nitrate supplementation is attenuated in cigarette smokers compared to non-smoking controls

Abstract

Dietary supplementation with inorganic nitrate (NO3−) has been reported to improve cardiovascular health indices in healthy adults. Cigarette smoking increases circulating thiocyanate (SCN−), which has been suggested to competitively inhibit salivary nitrate (NO3−) uptake, a rate-limiting step in dietary NO3− metabolism. Therefore, this study tested the hypothesis that dietary NO3− supplementation would be less effective at increasing the circulating plasma nitrite concentration ([NO2−]) and lowering blood pressure in smokers (S) compared to non-smokers (NS). Nine healthy smokers and eight healthy non-smoking controls reported to the laboratory at baseline (CON) and following six day supplementation periods with 140 mL day−1 NO3−-rich (8.4 mmol NO3− day−1; NIT) and NO3−-depleted (0.08 mmol NO3− day−1; PLA) beetroot juice in a cross-over experiment. Plasma and salivary [SCN−] were elevated in smokers compared to non-smokers in all experimental conditions (P < 0.05). Plasma and salivary [NO3−] and [NO2−] were elevated in the NIT condition compared to CON and PLA conditions in smokers and non-smokers (P < 0.05). However, the change in salivary [NO3−] (S: 3.5 ± 2.1 vs. NS: 7.5 ± 4.4 mM), plasma [NO3−] (S: 484 ± 198 vs. NS: 802 ± 199 μM) and plasma [NO2−] (S: 218 ± 128 vs. NS: 559 ± 419 nM) between the CON and NIT conditions was lower in the smokers compared to the non-smokers (P < 0.05). Salivary [NO2−] increased above CON to a similar extent with NIT in smokers and non-smokers (P > 0.05). Systolic blood pressure was lowered compared to PLA with NIT in non-smokers (P < 0.05), but not smokers (P > 0.05). These findings suggest that dietary NO3− metabolism is compromised in smokers leading to an attenuated blood pressure reduction compared to non-smokers after NO3− supplementation. These observations may provide novel insights into the cardiovascular risks associated with cigarette smoking and suggest that this population may be less likely to benefit from improved cardiovascular health if they increase dietary NO3− intake.