Pattern 04 / 12 Otto observes
Slightly low hydration → attention and memory affected
A 1.8% drop of body weight in water is enough to derail your day. You will not feel it as thirst.
Mild dehydration — a loss of just 1.5–2% of body mass in water — measurably lowers cognitive performance, sustained attention and working memory. Most people reach this zone without feeling thirsty.
Adan (2012) · Nutrition Reviews
Systematic review in healthy young adults: 1.8% dehydration reduced sustained-attention performance by a magnitude comparable to a 5-hour night of sleep.
Ganio et al. (2011) · Br J Nutr
Exercise-induced dehydration (1.5% of body weight) raised the perceived difficulty of cognitive tasks and lowered mood in young men, without significantly affecting physical tasks.
Rosinger et al. (2024) · American Journal of Human Biology
Under real-world ad libitum hydration, 29–39% of participants were classified as dehydrated (serum osmolality >300 mOsm/kg) at every assessment. Dehydrated participants performed about two-thirds of a standard deviation worse on a 14-minute sustained-attention task — a large practical effect in non-experimental conditions.
Katz et al. (2021) · J Acad Nutr Diet
A synthesis of the evidence shows that hypohydration — particularly through 24-hour fluid restriction — preferentially affects executive function, while other cognitive domains stay relatively spared. Thirst arises after cognitive performance has already started to drop.
The brain is ~75% water. Even small losses reduce neuronal cell volume and slow synaptic transmission. Thirst only kicks in around 2% dehydration — that is, after cognitive performance has already dropped.
If you wait to feel thirsty, you are late.
Water intake (logged manually or via other apps compatible with Apple Health / Health Connect) + body weight (smart scale) + activity level, to estimate real needs.
Simple rule: 30 ml of water per kg of body weight per day, plus 500 ml for every hour of exercise. For a 70 kg person without sport: ~2.1 litres.
Spread it across the day, not a litre all at once in the morning. Otto shows you where you stand, without sending notifications.
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