Cell phones may help busy executives keep in constant touch with important business associates, but they may also increase their risk of high blood pressure, preliminary research suggests. A study of 10 German mobile phone users found that when they switched on their phone, their blood pressure shot up by 5 to 10 millimeters of mercury, researchers reported in this week’s issue of the international medical journal, The Lancet. Exactly how cell-phone use can lead to increases in blood pressure is unclear, but researchers speculate that the electromagnetic fields emitted by phones may somehow boost pressure. While the blood pressure increases found in the new study are small, they may be detrimental to people who already suffer from hypertension, researchers led by S. Braune of the Neurologische Universitateklinik in Freiburg, Germany, explained.