The cause of his illness is unclear but a statement from his office said there was "no cause for worry" and that the length of his London stay would depend on advice from doctors. The vice president will be in charge.
Some 4.7 million people in northeast Nigeria depend on food aid, some of which is blocked by militant attacks, some held up by a lack of funding and some, diplomats say, stolen before it can reach those in need.
Buhari said the Presidency would personally supervise the performance of those entrusted with their welfare and commitments made by the Federal Government on their health, education, security and general well-being.
A thin-looking Buhari met the girls in the evening. "I can not express in a few words how happy I am to welcome our dear girls back to freedom", Buhari told them.
"We assure you of the government resolve to give comprehensive medical attention to the released schoolgirls and ensure their rehabilitation and reintegration into the society".
Boko Haram seized a total of 276 girls in the 2014 abduction.
Though Boko Haram has abducted thousands of people during its eight-year insurgency that has spilled across Nigeria's borders, the Chibok mass kidnapping in 2014 horrified the world and brought the extremist group worldwide attention.
The reception was attended by ministers, Service Chiefs and other government officials. The government would now look to securing the release of the remaining hostages, he added.
- The 82 freed Chibok girls are now in the capital, Abuja, to meet President Muhammadu Buhari, said a top official. Those released in October remain in government care in Abuja where they are getting medical attention, trauma counseling and rehabilitation, according to the government.
Around 270 girls were kidnapped in April 2014 by the Islamist militant group, which has killed 15,000 people and displaced more than two million during a seven-year insurgency aimed at creating an Islamic caliphate in northeastern Nigeria. Two more girls who successfully escaped have also since been discovered. Others did not want to come home either because they'd been radicalized by their captors.
Mr. Buhari stated this Sunday when he hosted the girls in his official residence at Aso Rock Villa, Abuja.
Girls Have Reportedly Been Released By Boko Haram
"Electricity has improved, price of petroleum products has stabilized, corruption has reduced to the barest minimum, Boko Haram is no longer in control of territories and the Niger Delta issue has been resolved", Shittu told his audience.
The released Chibok girls were due to arrive in Abuja on Sunday (yesterday).
"Three years is not three days", he said.
"The president has said that as numerous girls are alive, his administration will strive to get them back", Femi Adesina, a spokesman for the president, said. The president was expected to meet with the schoolgirls at 4 p.m. local time (1500GMT).
The International Committee of the Red Cross has tweeted what might be the first public image of the Chibok schoolgirls freed by Boko Haram extremists.
The number of Boko Haram suspects released by authorities remains unknown.
Boko Haram released 21 of the school girls in October 2016. He emphasized that he considered all 82 of the girls to be his daughters "because a lot of them worship in my church".
Garba Shehu said that Buhari will receive the 82 schoolgirls in Abuja who were freed Saturday after lengthy negotiations with Boko Haram.
The group representing the families of the girls said they were awaiting confirmation on how many had been released.
Statement from #BringBackOurGirls on release of 82 #ChibokGirls.