The Effects of Vitamin B6 Supplementation on Pain Thresholds and Tolerance

Sensory threshold will be measured using thermal stimulation (heat stimulation). The starting temperature of the applied probe will be adjusted to the individual's skin temperature and then slowly increased (0.5 deg C/s) until the participant feels a slight warm sensation. For safety, the temperature will never exceed 50 deg C. The procedure will be repeated three times. The average change in temperature (in degree Celsius) needed for participants to perceive a warm sensation will be used as outcome measure. Low values will therefore indicate a high sensitivity to warmth, whereas high values will indicate a low warmth sensitivity.

Pain threshold will be measured using thermal stimulation (heat stimulation). The starting temperature of the applied probe will be adjusted to the individual's skin temperature and then slowly increased (1 deg C/s) until the participant feels a slight pain/burning sensation. For safety, the temperature will never exceed 50 deg C. The procedure will be repeated three times. The average change in temperature (in degree Celsius) needed for participants to perceive a slight pain/burning sensation will be used as outcome measure. Low values will therefore indicate high pain sensitivity, whereas high values will indicate low pain sensitivity.

Pain sensitivity will be measured using electrical stimulation. Starting at an initial intensity of 0.3 mA, the intensity of each subsequently applied electrical stimulus will be increased in steps of 0.3 mA each, with a maximum intensity of 10 mA. The procedure will be continued until the participant perceives the applied shock as moderately painful (equivalent to a pain rating of 5 out of 10 or higher). The procedure will be repeated three times. The average intensity (in mA) needed for participants to perceive a moderate pain sensation will be used as outcome measure. Low values will therefore indicate a high sensitivity to electrical stimulation, whereas high values will indicate a low pain sensitivity in response to electrical stimulation.

Pain tolerance will be measured using thermal stimulation (heat stimulation). The starting temperature of the applied probe will be adjusted to the individual's skin temperature and then slowly increased (1 deg C/s) until the participant feels that they can't tolerate the heat anymore. For safety, the temperature will never exceed 50 deg C. The procedure will be repeated three times. The average change in temperature (in degree Celsius) needed for participants to reach their pain tolerance will be used as outcome measure. Low values will therefore indicate low pain tolerance, whereas high values will indicate high pain tolerance.

Pain tolerance will be measured by recording the number of seconds the participant is willing to keep their hand immersed in a 5 degree celsius cold bath, up to a maximum of 120 sec.

Pain sensitisation will be measured using a wind-up paradigm (temporal summation) with thermal stimulation (heat simulation).

The thermal probe will start at 32 deg C and increase in temperature (100 deg C/s) to 49 deg C. After a duration of 800 ms, the temperature will return to baseline. Participants will be asked for a pain rating on a scale form 0 (not painful) to 10 (extremely painful). Subsequently, a series of 10 heat stimuli (identical to the once above, ISI 400 ms) will be applied. Participants will be asked to rate the most intense pain that they felt across the series, using the same 0-10 rating scale. The difference in pain ratings in response to the series and to the single stimulus will be used as the outcome measure. Higher (positive) ratings will indicate a stronger sensitisation to repeated painful stimuli. In contrast, negative values will indicate habituation to repeated painful stimuli.

State anxiety will be measured using the State-Trait Anxiety Inventory (STAI), which produces a minimum score of 20 and a maximum score of 80, where higher scores indicate greater anxiety.

State positive and negative affect will be measured using the The Positive And Negative Affect Schedule Now (PANAS-N) (PANAS-N; adapted from Watson et al., 1988).

Sleep quality will be measured using the Pittsburgh Sleep Quality Index (PSQI), which results in a score ranging between 0 and 21, where higher scores indicate worse sleep quality.

Dietary intake will be measured using the Mediterranean Diet Adherence Screener(MEDAS), which produces a score ranging between 0 and 14, where higher scores indicate greater adherence to the Mediterranean diet.