The former first lady Laura Bush has opened a diplomatic can of worms by writing in her new book that she and her husband may have been poisoned during a state visit to a G8 summit in Germany in 2007.

The passage of Spoken From the Heart in which she discusses the incident amounts to the first time that the idea has been floated that George Bush's illness at the summit may have been the result of poisoning. The then US president succumbed to a stomach complaint, as did his wife and several members of their entourage, during a three-day meeting of world leaders in Heiligendamm.

The book is to be published early next month but a sneak preview of it was gained by the New York Times.

On Thursday 7 June 2008 the Bushes attended an official dinner at the summit along with other leaders of the industrialised countries that form the G8. The meeting at the Baltic Sea resort focused on the fight against Aids, malaria and other diseases affecting poor countries around the world.

The following morning the US president was reported sick and had to skip a couple of working sessions. Bush's adviser Dan Bartlett told reporters at the time that he was "very much under the weather", though his condition was "not serious".

"I'm not sure if it's a stomach virus yet or something like that, but he's just not feeling well in the stomach."

Nicolas Sarkozy, the newly elected president of France, said at the time that "Bush is slightly indisposed this morning and will rejoin the working meeting as soon as he can."

The US leader recovered sufficiently to be able to keep his appointment with Sarkozy, their first one-to-one meeting, later that day.

According to the New York Times, Laura Bush says that when the American delegation fell sick, the US secret service was called in to investigate but doctors put it down to a virus. "We never learned if any other delegations became ill, or if ours, mysteriously, was the only one," she writes.

There is no readily available record of what was served to the Bushes that Thursday night or who had access to the food. It is normal for the US secret service as a precaution against poisoning to prepare all meals for presidents travelling abroad, which adds to the mystery surrounding this visit.

In a memoir that appears to offer its share of revelations, Laura Bush also steps into an area of tragedy in her past which she has almost entirely avoided addressing publicly until now. On 6 November 1963, when she was 17, she was involved in a car crash in which her high-school friend Mike Douglas was killed.

The incident, in her home town of Midland, west Texas, was only reported for the first time in March 2000, when her and her husband were on the campaign trail during the presidential election that would see him enter the White House. She confirmed then that she had been driving the car that killed Douglas, and only spoke of the crash on one other occasion, telling the talkshow host Oprah Winfrey that she saw it as "a sign of the preciousness of life and how fleeting it can be."

In Spoken From the Heart Bush gives a much fuller and personal account of what happened. She, then Laura Welch, was driving her and a friend to a drive-in cinema in her father's car. They crossed over a stop sign and hit Douglas on the side of his vehicle, though he had had right of way.

"The whole time I was praying that the person in the other car was alive," writes Bush. "In my mind, I was calling 'Please, God. Please, God. Please, God,' over and over and over again."

According to the Times, Bush relates the intense feeling of guilt that she felt for years afterwards, particularly for failing to go to the boy's funeral which she said was at her parents' instigation. Instead, she slept through the ceremony.

Bush also says that the accident led to a prolonged period of deep spiritual doubt. "I lost my faith that November, lost it for many, many years. It was the first time that I had prayed to God for something, begged him for something … And it was as if no one heard. My begging, to my 17-year-old mind, had made no difference. The only answer was the sound of Mrs Douglas's sobs on the other side of that thin emergency room curtain."

The introspection induced by the tragedy may explain why Bush led such a low-key life through her twenties. She was working as a school librarian, aged 30, when she first met George Bush.

"Most of how I ultimately coped with the crash was by trying not to talk about it, not to think about it, to put it aside. Because there wasn't anything I could do. Even if I tried," she writes.

Her publishers, Simon & Schuster, say that the book also discusses her husband's struggle with alcohol and his decision to give up drinking.