The "sugar level by age chart" is not a real thing

Search "normal sugar level by age" and you will find dozens of neat tables: 70–100 mg/dL for a 20-year-old, 80–120 for a 40-year-old, 90–150 for someone over 60, and so on down the page. They look authoritative. They are shared on WhatsApp, printed by clinics and repeated by news sites.

No health authority publishes them. Not the World Health Organization, not the American Diabetes Association, not the Indian Council of Medical Research. The diagnostic thresholds — fasting 126 mg/dL, two-hour 200 mg/dL, HbA1c 6.5% — are the same number for a 25-year-old and a 75-year-old. There is no clause anywhere that raises the bar because a birthday passed.

Where the charts came from

Probably from two real things, mashed together and then copied from site to site until nobody remembered the original.

The first is observed average glucose. Average blood glucose in a population does drift upward with age, because insulin resistance and diabetes both become more common with age. That is a description of what is happening to a group of people, not a statement of what is healthy. Average waist circumference rises with age too; nobody publishes a chart saying a bigger waist becomes normal at 55.

The second is individualised targets for people who already have diabetes. Clinical guidelines really do say that treatment targets should be less strict for some older adults — someone frail, with several other conditions and a real risk of hypoglycaemia, is treated differently from a healthy 40-year-old. Those are treatment decisions, made by a doctor, for a person already diagnosed. They are not diagnostic thresholds and they are not a "normal range".

What genuinely does change

• Pregnancy. This is the one place where the numbers really are different, and they are lower, not higher. WHO's 2013 criteria diagnose gestational diabetes from a fasting glucose of 5.1 mmol/L (92 mg/dL) — a value that would be entirely unremarkable outside pregnancy. The pregnancy page has the full table.
• When to start testing. Guidelines differ on the age at which routine screening should begin, and Indian guidance generally starts earlier than Western guidance because type 2 diabetes appears at younger ages and lower body weights in South Asians. That is a question of who gets tested, not of what the result means.
• Which condition is likely. A child with very high glucose is more likely to have type 1 diabetes; an adult in their fifties is more likely to have type 2. That changes the investigation your doctor orders. It does not change the number on the threshold.
• Whether HbA1c can be trusted. Conditions that shorten red-cell survival — including some inherited haemoglobin disorders and iron-deficiency anaemia, both common in India — distort HbA1c at any age. More on that here.

So what should you read instead

The published criteria, which are on the main blood sugar levels page, and then your doctor. Not because that is a polite thing to say at the end of a web page, but because a fasting glucose of 118 mg/dL means something different in someone with a strong family history, a large waist and a raised blood pressure than it does in an otherwise healthy person, and no chart can see any of that.