Cold homes and stroke risk: practical clinical guidance for UK primary care

The link between cold indoor temperatures and cardiovascular events is one of the most stable findings in UK winter epidemiology. Cold drives blood pressure up, raises plasma viscosity, and increases the risk of thrombotic events in the days that follow exposure. Stroke is the specific endpoint that most closely tracks the indoor temperature signal, and the populations at greatest risk are the same populations most likely to be living in homes that fall below the WHO 18°C threshold during winter cold spells.

This article summarises the evidence in plain language, sets out the WHO and UKHSA thresholds, and gives a practical pathway for when a UK GP or practice nurse should consider a warm-home recommendation as part of cardiovascular risk management.

The mechanism in brief

Cold exposure produces peripheral vasoconstriction, which raises systemic vascular resistance and therefore blood pressure. The rise is proportional to the cold load and is measurable within hours. Plasma viscosity and fibrinogen concentrations rise on a slightly longer timescale, peaking at twenty-four to forty-eight hours of sustained exposure, which is one reason the excess in stroke and myocardial infarction tends to lag the cold spell rather than coincide with it. Older adults, people with hypertension, people with established cerebrovascular disease, and people on rate-control or anticoagulant regimens experience these shifts on top of an already-loaded baseline.

The temperature threshold matters. The WHO Housing and Health Guidelines (2018) recommend a minimum indoor temperature of 18°C for healthy adults during winter, with higher thresholds for infants, older adults, and people with chronic conditions. Below 18°C, blood pressure begins to rise; below 16°C, the prothrombotic shift becomes clinically meaningful; below 12°C, cumulative exposure carries a measurable excess risk of acute cardiovascular events.

What the UK data shows

Office for National Statistics data on Excess Winter Deaths (EWD) — the surplus of deaths in the four winter months over the average of the surrounding non-winter periods — has consistently shown that cardiovascular causes account for a substantial share of the winter excess. The EWD figure for England and Wales has varied year on year between roughly 17,000 and 50,000, with the size of the figure tracking both the severity of cold spells and the underlying condition of the housing stock.

The chart below shows indicative EWD figures for recent winters, rounded for clarity.

The 2020-21 spike reflects the pandemic period and is not a clean cold-housing signal; the surrounding winters give a more useful indication of the baseline. The point is that the figure is large, and a meaningful share of it is cardiovascular and cold-mediated rather than respiratory and infection-mediated.

Stroke-specific risk and the at-risk patient

Cohort studies that have examined stroke incidence against indoor temperature have shown a measurable increase in ischaemic stroke in the days following sustained exposure below 16°C. The effect is larger in people aged over 75, in people with established hypertension, and in people whose cardiovascular reserve is already compromised. The signal is smaller in younger, healthier adults but is not zero.

The table below sets out a practical risk stratification for use during winter pressure planning in primary care. The thresholds are not formal NICE recommendations; they are a synthesis of WHO guidance, UKHSA cold weather plans, and the clinical literature.

The 'warm home' prescription in practice

A warm-home prescription is not, in 2026, a formal entry on the FP10 pad. It is a written recommendation from the clinician — typically a short letter or a record entry that the patient can share — that states the clinical rationale for maintaining a minimum indoor temperature, identifies the patient as vulnerable for the purposes of energy-supplier Priority Services Register registration, and where appropriate signposts the household to the ECO4 grant scheme and to a PAS 2035 retrofit assessor.

The components a warm-home prescription should include are: the patient's clinical condition in plain terms, the WHO 18°C threshold and why it matters for this patient, a recommendation for Priority Services Register registration, and a referral or signposting line for retrofit assessment. The prescription is most effective when it is written in language the household can use directly with their energy supplier and with a retrofit assessor — the audience is not the next clinician.

Several integrated care boards in England have piloted formal warm-home referral pathways with their local authority partners, and the early evaluations indicate that uptake correlates closely with the workflow ergonomics in primary care rather than with the underlying eligibility of the patient population. Where the referral is a single tick-box in the EMR with templated downstream paperwork, uptake is high; where it requires a free-text letter and external lookup, uptake is low. The implication for practices considering implementing the pathway is that the engineering of the workflow matters as much as the clinical case for it.

ECO4, GBIS and the route to a warmer home

The Energy Company Obligation 4 (ECO4) scheme, running to March 2026, has been the principal mechanism for fully or partly funded retrofit works in low-income households. Its successor — the Great British Insulation Scheme (GBIS) for single-measure works and the Warm Homes Plan for whole-house approaches — extends the basic logic. Eligibility is typically a combination of receipt of qualifying benefits, low income, and an EPC rating below a threshold, with Local Authority Flexible Eligibility (LA Flex) routes for households that fall outside the standard tests but are judged vulnerable on health grounds.

The clinical relevance is that LA Flex pathways typically accept a clinician's letter as part of the evidence base. A short letter identifying the patient as vulnerable to cold exposure on cardiovascular grounds, stating the WHO 18°C threshold, and naming the condition is generally sufficient. The letter does not need to specify the works to be undertaken — that is the retrofit assessor's role under PAS 2035.

Practical anticipation and the autumn clinic

The cardiovascular literature on cold exposure is consistent on one operational point: the right time to act on a patient's housing is before the first cold spell, not during it. The pathway from a clinician's letter to a warmer home runs through energy-supplier registration, retrofit assessment, ECO4 application, design, installation, and commissioning — typically a process of months rather than weeks. A patient flagged in October is plausibly in a warmer home for the January cold snap; a patient flagged in January will see no benefit from the works that year.

The implication for primary-care annual review scheduling is that cold-housing concerns sit naturally in autumn appointments rather than in spring or summer ones. Several practices have begun routinely asking the warm-home screening question as part of the autumn hypertension review, the autumn diabetes review, and the autumn frailty assessment. The marginal time cost is small, the disclosure rate is meaningful, and the pathway behind it is now well-trodden.

For the highest-risk patients — recent stroke, recent MI, severe hypertension, advanced heart failure — the calculus is sharper. These patients' winter cardiovascular events are rare, devastating, and partially preventable. A warm-home letter, a Priority Services Register registration, and a retrofit referral in October is a reasonable secondary-prevention intervention to add to the medication review.

What success looks like, and what to measure

For practices considering implementing a warm-home pathway as a routine offer, the operational measures that matter are: the proportion of high-risk patients asked the screening question during the autumn review window; the proportion of those who disclose a warm-home concern; the proportion of disclosures that result in a documented onward referral; and the proportion of referrals that result in completed works before the following winter. The fourth measure is the one most clearly outside the practice's control, but tracking it across multiple winters gives a useful indication of whether the local retrofit infrastructure is functioning.

Health outcome measures — winter cardiovascular admissions, primary care contact frequency, blood pressure control — are too noisy at the practice level to detect a signal in any single year, but at PCN or ICB scale and across multiple winters, the evaluations of analogous schemes have generally shown modest but real reductions in winter pressure on secondary care.

The cold-homes-and-stroke pathway is one of the clearest cases in UK primary care where a housing intervention can be expected to produce a measurable cardiovascular benefit. The threshold is 18°C, the vulnerable groups are well-defined, and the mechanism by which a clinical recommendation translates into a warmer home is now reasonably well-trodden through ECO4 and PAS 2035. The act of writing a short warm-home letter, registering a patient on the Priority Services Register, and signposting a competent retrofit assessor takes minutes in a consultation and is one of the more durably useful actions a GP can take in the autumn clinic.