What is nitrate poisoning?
Nitrate and nitrites pose a serious health risk. In breastfed babies, exposure to 5 mg nitrite per kg may lead to food poisoning.
High nitrate levels of vegetables may cause nitrate poisoning, especially in babies. Nitrate does not have a direct toxic effect. However as nitrites are formed from nitrate in the digestive tract of humans and ruminants by bacteria, intoxication occurs. Nitrate is absorbed by blood and oxidizes hemoglobin iron and oxygen cannot be carried to body tissues.
The amount of nitrate and nitrite varies depending on the land, rainfall and soil and manure used to grow vegetables.
Nitrate poisoning is not a frequently seen condition nowadays. However it is always better to learn and be cautious about it. It is said that nitrate poisoning can cause "Blue baby syndrome".
What foods may contain nitrate?
In general, root vegetables and green leafy foods contain nitrate. Nitrate level in these foods changes according to the soil where vegetables are grown, the climate and the manure used while growing them.
Babies younger than 3 months old should never have foods like carrot, cabbage, broccoli, spinach, beetroot, turnip, and savoy cabbage. If fed with those, nitrate poisoning may occur.
Which babies are exposed to risk of nitrate?
Foods mentioned above cannot be fed to babies around 3 months old and should not be given before babies are 6 months old.
Usually after babies are 6 months old, their stomachs will be developed enough to cope with the bacteria and nitrate levels.
Stomach anatomy in adults can handle nitrates in vegetables. However sometimes this is not the case for babies and this may cause "blue baby syndrome". 

What are the symptoms of nitrate poisoning?
The clearest symptom of this syndrome is blue discoloration of lips and skin around the eye. Any baby with this syndrome should be taken to the doctor immediately. Still, don’t panic and stay calm to support your baby. Don’t forget that nitrate poisoning is treatable. 
What should you do?
If you want to prevent nitrate accumulation in babies, do not use the water used to boil nitrate-containing vegetables, to produce formulas. Boil vegetables that contain nitrate separately and throw away the boiling water. Because most of the nitrate that the vegetable contains passes to the water during boiling. This is a simple and easy way to prevent poisoning.