What goes into the child's flask gets decided in the morning. Through the summer it was barley tea and settled; as the weather cools, the question comes back. What is in the house is hojicha, and the back of the packet gives ingredients and some words about roasting. The material for the decision is outside the packet.
How far the figures at hand reach
As far as roughly how many mg are in one particular cup. How many cups is not something this book decides, and public bodies have not set an acceptable daily intake (ADI) for caffeine. What can be put in its place is a way of working out the figure for the cup in the cupboard, plus the figures some agencies publish as daily totals.
Why no acceptable daily intake has been set
The Food Safety Commission of Japan writes that sensitivity to caffeine differs greatly between individuals, which makes the effects on health difficult to assess accurately, and that no acceptable daily intake has been set. The MHLW writes that, largely because individual differences are great, none is set in Japan or internationally. The absence is not a sign that the question has gone unexamined, but that it will not sit in one number.
What the ministry pages introduce are overseas figures
On that footing, the ministry pages introduce figures from overseas bodies: EFSA (2015), Health Canada (2010), the World Health Organization (2016). Each body, and each group of people, has its own value (table below). None is a standard set by Japan; all are overseas figures, introduced as such.
Two things come before reading them. First, every figure introduced is a daily total, not a per-cup value: it covers everything taken in from food across one day. Coffee, black tea, soft drinks and caffeine-containing medicines all fall inside the same day. Second, the adult figures are amounts per day and the children's are per kilogram of body weight. The units differ, so neither serves as a guide to the other. The Consumer Affairs Agency, introducing Health Canada's figures, adds that even where this amount is exceeded, it does not necessarily follow that health will be adversely affected.
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 300 mg a day or more | mg per day |
One item introduced for the night
For the night, one item is introduced. Taking 100 mg immediately before bed (about 1.4 mg per kg of body weight for an adult of 70 kg) may cause sleep disturbance in some adults — a 2017 assessment by AGES, the Austrian Agency for Health and Food Safety, carried in the Food Safety Commission's factsheet.
Coming down from the figures to one cup
Coming down from the figures to one cup means multiplying concentration by volume. Tea brewed under the published value's conditions holds 20 mg in 100 mL, so a 150 mL cup holds 30 mg [calculated].
Does brewing it weaker bring it down, then? Public data on how hojicha moves when the strength or the water temperature changes did not turn up in this search. The line that brewing can adjust it cannot be written from the material in this chapter.