In the morning, the question of what goes into the child's flask. All summer it was barley tea; as the weather cools, the doubt comes back. The hojicha packet in the cupboard, turned over, gives only ingredients and a few words about roasting. What the decision needs lies outside the packet.
What follows looks at why no upper limit has been set, how the figures being introduced should be read, and how to work out the amount in one cup.
No daily limit has been set
The calendar on the kitchen wall is crowded with the child's plans. For caffeine, no upper limit on a safe daily amount has been set.
The national food safety body writes that sensitivity varies greatly between people, which makes the effects on health hard to assess accurately. The health ministry, too, says that largely because of those differences none is set, at home or internationally. The absence does not mean the question was never studied; it means the answer will not sit in one number.
What can be said here goes as far as roughly how much is in one cup. How many cups is not decided in these pages. In place of a limit, what is introduced are the figures of overseas bodies.
A day's total, not a cup's
A tin of coffee and a box of black-tea bags stand on the same shelf. The overseas figures introduced on the ministry pages are amounts taken in across a whole day, from all food and drink.
The figures are set separately for each body and each group of people. None is a national standard; each is introduced as an overseas body's value. Coffee, black tea, soft drinks and medicines containing caffeine all count within the same day.
The adult figures are amounts per day; the children's are per unit of body weight. The units differ, so one cannot serve as a guide for the other.
The consumer agency's page adds that going over the figure does not necessarily mean harm to health. After the daytime comes the cup at night.
Figure 1-3-1The overseas caffeine guides being introduced (daily totals taken in from all food, not per-cup values)
| Body | Year | Population group | Value | Unit |
|---|---|---|---|---|
| European Food Safety Authority | 2015 | Healthy adults | 400 mg | mg per day |
| European Food Safety Authority | 2015 | Healthy adults (single dose) | 200 mg | mg per single dose |
| European Food Safety Authority | 2015 | Pregnant and breastfeeding women | 200 mg | mg per day |
| European Food Safety Authority | 2015 | Children and adolescents | 3 mg | mg per kg of body weight per day |
| Health Canada | 2010 | 18 and over | 400 mg | mg per day |
| Health Canada | 2010 | Ages 4–6 | 45 mg | mg per day |
| Health Canada | 2010 | Ages 7–9 | 62.5 mg | mg per day |
| Health Canada | 2010 | Ages 10–12 | 85 mg | mg per day |
| Health Canada | 2010 | 13 and over | 2.5 mg | mg per kg of body weight per day |
| World Health Organization | 2016 | Pregnancy | A caution on high intake of more than 300 mg a day | mg per day |
One assessment, before bed
At night, a thin thread of steam rises straight from the cup. For the night, only one assessment is introduced.
A hundred milligrams taken in one go just before bed may disturb sleep in some adults, it says. It is an overseas body's assessment, introduced in a national committee's factsheet.
The sources go as far as this single assessment. After the figures comes the cup in hand.
How much in one cup
The usual cup comes out of the cupboard and sits in the palm. The amount in it is the strength of the tea multiplied by the size of the cup.
For hojicha brewed the way the national table brews it, divide the cup's millilitres by five to get milligrams. A bigger cup holds more. With more leaf in the same water, the real cup comes out higher than this.
Whether brewing it weaker brings it down is not covered by any public data measured on hojicha. That brewing can adjust it cannot be written from the material at hand. Pregnancy, children and the cup before bed each have a piece of their own: hojicha in pregnancy and breastfeeding, hojicha for kids and hojicha before bed. The figures and conditions are gathered just below. The flask lid clicks shut, a small sound in the kitchen.
The numbers in detail
- Acceptable daily intake
- The Food Safety Commission of Japan states that no acceptable daily intake (ADI) has been set for caffeine. The reason given is that individual sensitivity varies greatly, making health effects hard to assess accurately.
- Health ministry
- The MHLW also writes that, largely because of individual differences, none is set in Japan or internationally.
- Overseas figures
- The ministry pages introduce figures from EFSA (2015), Health Canada (2010) and the World Health Organization (2016). Values by body and group are in the table in the text.
- Adults and children
- For adults, EFSA and Health Canada both give 400 mg a day. For children and adolescents, EFSA gives 3 mg per kg of body weight a day.
- Consumer agency note
- The Consumer Affairs Agency, introducing Health Canada's figures, adds that exceeding this amount does not necessarily mean health will be adversely affected.
- Night-time assessment
- The night-time assessment is from AGES, the Austrian Agency for Health and Food Safety, in 2017. Taking 100 mg once just before bed (about 1.4 mg per kg for a 70 kg adult) may cause sleep disturbance in some adults. The source is the Food Safety Commission's factsheet.
- One cup
- The cup calculation assumes infusion brewed under the published conditions at 20 mg per 100 mL, that is 1 mg per 5 mL. A 150 mL cup then holds 30 mg [calculated].