I'm conducting an N=1 self-experiment, starting today, to try to gain evidence for or against the idea that taking a multivitamin causes me to gain weight. The experiment will run for about 6 months and will alternate between 30 day phases where I take a multivitamin and where I'm not taking the vitamin. For each phase, I will record my weight on the morning starting the phase, and then record the delta from that first point for each subsequent day.

To determine how to resolve this market, I will use R to fit linear models to both the three vitamin taking phases and the three non vitamin taking phases. I will use R to compute the 95% confidence interval for the coefficient on the day variable. If the lower bound of the vitamin confidence interval is greater than the upper bound of the non-vitamin confidence interval and greater than zero, then I will resolve this market as YES. Otherwise, it will resolve as NO.

The multivitamin I'm taking contains the following:

• Vitamin A: 180mcg

• Vitamin D: 50mcg

• Vitamin E: 6.7mg

• Folate: 200mcg

• Vitamin B12: 8mcg

• Magnesium: 30mg

• Zinc: 2.4mg

• Omega-3 DHA: 333mg

• Boron: 0.7mg

• Vitamin K2: 90mcg

The experiment should run for about six months. I have some travel planned during that time. I'm not planning on packing a scale when I go, so I will not record weights during travel and for two days afterwards. If I travel during a vitamin phase, I will keep taking the vitamin during the trip. If a phase ends during a trip, I will just count the data collected before the trip started, and I will delay the start of the next phase until two days after the trip ends. I've set the end date for this market based on the schedule if I don't have to delay any phase starts. If I do delay a phase start, I'll adjust the end date accordingly.

While I'm attempting to make this as scientific as possible, N=1 studies are inherently limited. Obviously the experiment is not blinded, and I have a pretty strong prior that the multivitamin does cause weight gain, so the setup is prone to see weight gain during the vitamin phases caused by a placebo effect.

Today (2025-04-25) I started a vitamin phase, and in 30 days I'll end that phase and begin a non-vitamin phase. I previously was taking this multivitamin for a couple years, but I tapered off and stopped taking them during the second half of last year. Until this morning, I had not taken the multivitamin this year.

• Update 2025-04-30 (PST) (AI summary of creator comment): The creator has updated the resolution criteria slightly. The market will now resolve YES only if both of the following conditions are met:

  • The lower bound of the 95% confidence interval for the daily weight change coefficient during the vitamin-taking phases is greater than the upper bound of the 95% confidence interval for the daily weight change coefficient during the non-vitamin-taking phases.

  • The lower bound of the 95% confidence interval for the daily weight change coefficient during the vitamin-taking phases is also greater than zero.

Otherwise, the market will resolve NO. This change ensures that the market resolves YES only if there is statistical evidence of actual weight gain (a positive trend) during the vitamin phases, rather than just a slowing of weight loss compared to non-vitamin phases.