Ionized magnesium variation is measured during a normal day and again during a day with an exercise protocol of 90 minutes.

Magnesium is an essential micronutrient for health and exercise performance. Deficiencies are common, especially in case of insufficient diets. Athletes are a population at risk of magnesium deficiency, as they can have strong nutritional (dis)believes and increased losses through sweat. That is why monitoring magnesium status in athletes is very important. Ionized magnesium is the active form of total magnesium, this value might be even more important than total magnesium. However, whether ionized magnesium is influenced by day variation is not clear yet. In addition: one bout of exercise can change magnesium status and probably ionized magnesium status. For people active in sports it is important to be aware of this variation in magnesium status, to prevent the diagnosis of false inadequate magnesium status. Therefore it is the aim of this proposal to determine whether ionized magnesium varies within one day and whether it changes after an acute bout of exercise.

Objective:

The main objective is to investigate whether ionized magnesium concentration varies during one day, and whether it is changed after one bout of exercise

Study design:

This will be a cross-over design. With screening and preliminary tests before the exercise test day and the non-exercise test day. The order in which exercise day and non-exercise day will be done, will be randomly divided between the participants.

Intervention:

A rest day and an exercise day At exercise day: an exercise test of 90 min at 70% of VO2max. Blood samples are taken at set time points during rest day and exercise day

Inclusion Criteria:

• Age: 18 - 45 y
• BMI: 18.5 - 25
• Minimal of 5 hours of training per week, for at least 2 years
• Used to bike, at least 5 hours per week in high season
• No Mg and / or Ca supplementation during study
• No blood donation, during or in the 6 weeks preliminary the study
• Suitable veins
• No chronic medication, with the exception of paracetamol and or birth control
• No antibiotics in the month preliminary the study
• Good health
• Serum Mg > 0.7 mmol/L
• Willing to give blood
• Able to be present and participate at all test days

Exclusion Criteria:

• Chronical illness
• Use of medication with the exception of paracetamol and or birth control
• Mg and or Ca supplementation use
• Inadequate Mg intake (according to FFQ)
• Working at Human Nutrition
• Wageningen University Msc thesis or internship at Human Nutrition
• Participating in other scientific research (with the exception of EetMeetWeet)

Participants receive a letter with their personal information. VO2max, body weight and height, total Magnesium and ionized magnesium will be communicated.