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A diabetic mother claims she could have been put in a coma by the high sugar content of a Starbucks latte.

Liz Adams experienced dizziness and headaches after the ‘grande' 473ml drink.

The 46-year-old found her blood sugar was four times her healthy level – forcing her to take two shots of insulin for fear of falling into a coma.

Bank manager Adams initially feared that sugar or syrup may have been added to the coffee by mistake.

But the married mother-of-one later found the coffee's sugar content was simply due to the amount of steamed milk. According to Starbucks' website, the ‘grande' latte contains 16.5g of sugar – almost half the amount that is found in a 330ml can of cola.

Adams, a Type 1 diabetic  from Dukinfield, Greater Manchester, had been returning home from a holiday in Cornwall with her fireman husband Paul when she bought the coffee at services on the M5 in Gloucestershire.

Starbucks said the sugar was naturally occurring.

But Adams said: ‘I'm just shocked. I could have gone into a diabetic coma and died.

‘I think I managed it well due to the fact that I've been type-one for 28 years. 

‘Someone younger wouldn't have known what to do.

‘I wouldn't drink half a can  of coke, which has the same sugar content, except when I need  to raise my sugar levels if they went low – so why would I want to drink the same amount of sugar in a latte? 

‘It's just coffee beans and  milk, which I know has carbohydrates, but I didn't expect it to have so much sugar – or any at all really. So it should be clearly labelled because 16.5 grams is a lot of sugar.' 

Her blood sugar level returned to normal the next day and she contacted Starbucks to complain.

She said the chain told her it was ‘investigating' and offered her a chart showing the sugar content in their drinks. Mrs Adams said: ‘I'm never drinking from Starbucks ever again. I want other people to know the content of the drinks before they buy them.

‘Drinks need to be labelled and people need to be aware how much sugar is in their drinks.

‘Luckily I didn't go into a diabetic coma. 

‘If your sugars run too high you can have organ damage and even body parts can drop off due to lack of blood circulation.' 

Very similar levels of sugar are contained in rival High Street coffee chains' lattes of the same size.

Lower sugar options are available by changing the type of milk, for example, a ‘grande' latte with soy milk contains 8g of sugar.

Simon Redfern, of Starbucks, said: ‘We were concerned to learn of this customer's experience in our store. 

‘Starbucks lattes are made as standard with two shots of espresso and semi-skimmed milk, which contains naturally occurring lactose. No sugar is added to a standard latte.' 

He said all nutritional information about Starbucks' products was available on its website and mobile phone app, while baristas could answer questions in stores.