Morning stiffness is common, and rarely means damageEmerging evidence
Back pain is very common and usually improves within a few weeks, the NHS says, and stiffness first thing is part of ordinary back pain for many people. Arthritis UK says "Back pain isn't usually caused by arthritis", and that "it's usual for your back to get stiffer as you get older".
In 675 adults with back pain, on average 66 years old, worse morning stiffness went with narrowing of several discs, not with C-reactive protein (CRP), a blood marker of inflammation: morning stiffness looked more like a sign of wear than of inflammation. Disc wear is common in people with no pain at all, from 37% of 20-year-olds to 96% of 80-year-olds, so it isn't a sign of damage on its own.
Sources 1, 2, 3, 4
Why mornings: the discs take up water overnightEmerging evidence
Lying down unloads the spine and the discs take up water. People are about 19 mm taller on waking, and in two small studies more than half of the day's height loss happened in the first hour after getting up; in a third, the first hour showed the biggest change. Lumbar disc volume falls about 16% over a day's activity on magnetic resonance imaging (MRI). People with chronic back pain go through the same daily cycle as people without it (about 18 mm in both), so it's normal, not a faulty disc.
In laboratory and cadaver work, the lower spine bends about 5 degrees less early in the morning, and bending forward then puts about 300% more stress on the discs, and 80% more on the spine's ligaments, than later in the day. That's a mechanism, not proof that morning bending causes pain.
Sources 5, 6, 7, 8, 9, 10, 11
Inflammatory back pain: the pattern to recogniseStrong evidence
Axial spondyloarthritis, which includes ankylosing spondylitis, is inflammation of the spine and pelvis. The NHS says it usually starts between 18 and 40, that the pain gets better with exercise but not with rest, that pain and stiffness are worse in the morning and at night, and that it can wake you during the night. The National Institute for Health and Care Excellence (NICE) says it affects a similar number of women as men, and can be there despite a normal X-ray and a negative blood test for the human leukocyte antigen B27 (HLA-B27) gene marker.
No single feature separates it from ordinary back pain. International expert criteria use 5 features (improvement with exercise, pain at night, a gradual start, starting before 40, and no improvement with rest), and 4 of the 5 picked out about 80% of people with it in a study of 648, with some false alarms. A review in the British Journal of General Practice reports that most people's symptoms start before 45, and that the average delay to diagnosis in the UK has been 8.65 years; a systematic review found typical delays of 2 to 6 years.
Sources 12, 13, 14, 15, 16, 17, 18, 19
The 30-minute line, and its limitsEmerging evidence
Stiffness that eases within about half an hour fits ordinary back pain and arthritis: NICE diagnoses osteoarthritis with no morning stiffness or stiffness lasting "no longer than 30 minutes". Stiffness for more than 30 minutes is one of four features of inflammatory back pain in one set of research criteria, and a question on a checker from the National Axial Spondyloarthritis Society.
On its own it isn't a diagnosis: in older adults, how bad the stiffness was went with disc wear, and NICE's referral list doesn't use morning stiffness at all. It uses starting before 35, waking in the second half of the night, buttock pain, improvement with movement or within 48 hours of anti-inflammatory painkillers, a family history, psoriasis, arthritis and pain where tendons attach to bone.
Sources 20, 15, 17, 3, 12
Night pain on its own is rarely seriousEmerging evidence
In 482 people at a back pain triage clinic, 213 had night pain (90 of them every night) and none was found to have a serious disease. What matters is the company it keeps: the NHS asks you to see a GP if back pain doesn't improve after resting or is worse at night, and NHS inform adds pain that isn't affected by movement.
Sources 21, 1, 22
When a scan or test helpsStrong evidence
Not for ordinary morning back pain: NICE says don't routinely image low back pain, and disc changes are common without pain.
For suspected axial spondyloarthritis, the rheumatology referral decides: NICE asks specialists to start with an X-ray of the joints at the back of the pelvis and, if that's normal, a special MRI scan, with the HLA-B27 blood test where needed. A GP may do that blood test if exactly 3 of NICE's referral features are present. Inflammation markers and HLA-B27 can be normal, especially in women. For a suspected kidney infection, the GP tests your pee.
Sources 23, 4, 12, 18, 24
How it usually goesEmerging evidence
Ordinary back pain usually improves within a few weeks, the NHS says, and NHS inform says most problems improve within 6 weeks. In the morning-bending trial, people with persistent or recurring back pain improved once they cut down bending early in the morning, and at 3 years those who kept it up had improved further. Inflammatory back pain doesn't settle on its own, and diagnosis opens up specialist treatment. No one can promise a date.
Sources 1, 22, 25, 26, 19