Nitrate levels in organic lettuce are far lower than levels found in conventional greenhouse lettuces, claim Finnish researchers. A study in the west of the country claims to have found sharp differences in the nitrate levels of organic and conventional lettuce. Nitrate occurs naturally in most plants and vegetables, but the amount of nitrate can be affected by fertilisers, growing conditions and the amount of light. An excessive amount of nitrates has been linked to a reduced ability of the blood to carry oxygen. Around 1% of produce sold in Finland shops is organic, much lower than in some other European countries.