Article and comment – Living by the numbers
There are a few health “numbers” that we take for granted and live by. This is without always knowing the origins or whether these are facts or convention we have excepted over time:
Brushing your teeth twice a day:
Although this is recommended by England’s public health, the national service providing this recommendation is unsure of the origins. In 2012, the Academic Centre for Dentistry Amsterdam showed that brushing your teeth for 1 minute removes 27% of plaque bacteria, whilst brushing for 2 minutes removes 41% of bacteria. Most people brush their teeth for only 45 seconds, therefore the amount of time you spend brushing your teeth may be more important that the number of times you brush your teeth. However, 41% of plaque removal is still quite low. Daily flossing can further remove bacteria, as brushing only removes plaque from the front and back of teeth. In a 2006 study, when comparing 51 twins, flossing reduced gum bleeding within 2 weeks by 38%. Compared to not flossing, however, the study did not mention how much more bacteria flossing removes compared to brushing alone.
10,000 steps a day:
This, as a number, is definitely a convention, developed by Pedometer researcher Dr Catrine Tudor-Locke in Japan. It is not based on research, but as a general indicator of activity when the average amount of steps taken by people in Western society is 3000. In a 2019 study, epidemiologist I-Min Lee from Harvard University found that the overall mortality rate directly reduced when step count increased from 3000 steps to 7500 steps a day. There was little further improvement beyond this amount. However, the factor that made a bigger difference was the speed of walking rather than the number of steps. Walking at a pace that means that you are “Somewhat puffed” or “Can not easily hold a conversation when walking” for 30 minutes is more important than the number of steps taken per day for fitness and health.
Drinking 8 glasses of water a day:
This number is based on the US Food and Nutrition Board dietary recommendations of consuming 1 millilitre of water for every calorie consumed. This is equivalent of about 2 litres a day for an “average” 2000 calories (8368 Kilojoule) diet, published in 1945. However, firstly, 30-35% of water is already consumed from food and does not need to be further “drunk” as water. Secondly, people are different in size and in food intake, therefore water needs are different. Your personal water balance is governed by a feedback loop between your kidneys and your brain, through antidiuretic hormone vasopressin. Listening to your body and drinking when you are thirsty may still be the best guide.
8 hours of sleep a day:
This is still the ideal average recommended for adults. People who have less than 7 hours of sleep have higher overall mortality rates. Those who have less than 5 hours of sleep have a much higher mortality rate than those who have more than 8 hours of sleep. Having the ideal amount of sleep is liked to optimum cognitive functioning, improved mood, alertness and improved reaction time.
Eating 5 serves of fruit/vegetables a day:
This is one where, the more the better. 5 serves is based on the WHO’s recommendations of 400 grams a day, with a serve (80 grams) being equivalent to about a small orange or a carrot. Fruits and vegetable contribute to our intake of vitamins such as Vitamin A, C, Folate, Dietary Fibre (soluble and insoluble) and water. Eating this quantity reduces the risk of coronary heart disease, stroke and heart disease by 14% (compared to 2.5 serves). However, eating 10 serves reduced risk by 24%. In addition, certain fruits and vegetables are more beneficial than others. In particular, apples and pears, cruciferous vegetables such as cabbage and kale, berries and citrus fruits.
Tait, A (2021) Living by the numbers. New Scientist, 11th September 2021, No. 3351. P38-41.
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