What are the common misunderstandings about mattress firmness?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
The belief that "a hard mattress is good for your back" is especially deep-rooted in Japan, tied to the tradition of a thin futon (*shikibuton*) laid on tatami. Outside Japan the opposite view, "the softer, the more comfortable", is common. Here we sort out only what can be said with confidence, from back-pain research and the general guidance of the bedding industry.
Points to judge by
| Item | Detail |
|---|---|
| Research | A widely cited randomised trial (Kovacs et al., *Lancet* 2003) found a medium-firm mattress better than a firm one for pain and sleep quality in patients with back pain |
| Guide | No gap under the lower back and back when lying on your back; spine parallel to the floor when lying on your side; easy to turn over |
| Body weight | Lighter people tend to suit a softer mattress, heavier people a firmer one, in terms of how far the body sinks |
| Sleeping position | Side sleepers need enough softness for the shoulder and hip to sink; back sleepers, slightly firmer |
| Futon on tatami | A thin futon is too hard and concentrates pressure on the hips and shoulders. Use 3–5 cm or more of thickness, or a mattress underneath |
| Replacement | Sagging (body impressions that do not spring back), hips sinking, back pain in the morning. Guide: 7–10 years |
- Japan's traditional shikibuton is thin and hard, which is generally described as the origin of the idea "hard = good for the back"; but today's general guidance from orthopaedics and the bedding industry is "medium".
- The Japanese Orthopaedic Association advises, on back pain, that bedding should "not let the body sink in, and should make turning over easy".
- The combination with your pillow decides the alignment of neck and spine (see our article on pillows).
[Verify] The research citation is Kovacs FM et al., Lancet 2003; 362:1599-1604. Check the Japanese Orthopaedic Association's wording.
Misunderstanding 1｜A hard floor or board is good for back pain
Too hard, and pressure lands on single points at the hips and shoulders; you turn over more and sleep more shallowly. In the research, medium-firm came out ahead.
Misunderstanding 2｜The softer, the more comfortable and the better for your body
Sink in too far and the lower back is held in a bent position, and turning over becomes harder. One cause of a stiff lower back in the morning.
Misunderstanding 3｜The more expensive the mattress, the better for your body
Price and fit are two different things. Fit depends on weight, sleeping position and preference; the practical approach is to lie on it in the shop for 10 minutes or more and choose a product you can return if it does not suit you.
Misunderstanding 4｜A mattress never needs replacing
Sagging reduces how well it works. 7–10 years, or when body impressions no longer spring back. Rotating it head-to-foot and flipping it regularly makes it last longer.
Misunderstanding 5｜Laying the futon directly on tatami is the correct Japanese way
A single thin futon is often too hard; the usual practice today is to put a mattress or a thick under-pad beneath it. Moisture control (a slatted *sunoko* base, or lifting and airing the futon) is also needed.
---
Sources
- Japanese Orthopaedic Association, *Low back pain* [腰痛] (daily-life precautions, bedding)
https://www.joa.or.jp/public/sick/
- Kovacs FM, et al. "Effect of firmness of mattress on chronic non-specific low-back pain." Lancet. 2003;362(9396):1599-1604.
https://pubmed.ncbi.nlm.nih.gov/14630439/
- Ministry of Health, Labour and Welfare, *Sleep Guide for Health Promotion 2023* [健康づくりのための睡眠ガイド2023] (bedroom environment)
https://www.mhlw.go.jp/content/10904750/001181265.pdf
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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