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© dailymail.co.uk'Ticking timebomb': Teenage girls' junk food diets are harmful.
A typical teenager probably thinks nothing of a diet packed with pizza, sweets and sugary drinks.

But by that age what they eat is already taking a severe toll on their health, research shows.

Millions of teenagers are dangerously low in key vitamins and minerals, experts have warned - with girls faring worst.

An appetite for junk food is feeding a 'ticking timebomb' of disease and ill health, researchers have concluded.

They found teenagers of both sexes were among the biggest guzzlers of salt, alcohol and sugar-laden soft drinks.

At the same time, they shun fruit, vegetables and oily fish. Almost half of teenage girls are dangerously low in iron, magnesium and selenium. Iron, found in red meat, liver, beans, nuts and green leafy vegetables, is vital for the production of healthy red blood cells and helps keeps memory and attention sharp.

Magnesium, from shellfish, whole grains and nuts, helps keep bones strong, while selenium keeps the immune system healthy.

One in ten girls is dangerously low in calcium, putting them at risk of brittle bones and falls and fractures in old age. And one in six is severely short of iodine, a mineral key to brain development in the womb.

Teenage boys are also a concern, with one in ten lacking in zinc, which is key to the production of sperm, the healing of wounds and the recovery of muscles after exercise.

The researchers believe teenagers' diets are particularly bad because they are starting to feed themselves for the first time, often skip meals and many are starting to experiment with cigarettes, which cut appetite.

In addition, many girls will be on spurious diets which advise cutting out certain foods to keep them slim or their skin glowing.

Carrie Ruxton, an independent nutritionist, and Emma Derbyshire, a nutritionist at Manchester Metropolitan University, crunched together the results of 38 studies into diets and their consequences for health.

Dr Ruxton said:
'While things like heart disease and cancer affect people in their 40s, 50s and 60s, the very early stages happen several decades before.

'It may be boring thinking about your health when you are 14, 15, or 16, but it is really important to lay down the balanced diet you are going to follow of the rest of your life.'
They conclude in the journal Complete Nutrition:
'The diet quality of teenagers and young adults is fundamentally important. During this life-phase, dietary requirements may be high due to rapid physical and mental development.

'Unfortunately, this is often hampered by social factors, body image concerns and the fact that many young people "live for the minute", being unaware of how current diets can affect later health.

'To many young people, middle age and the risk of chronic disease impacting on their life may seem far off. But the foundations of conditions such as cardiovascular disease are laid in childhood.'
The analysis was funded by the Health Supplements Information Service.