Quarantine during COVID-19 outbreak: Changes in diet and physical activity increase the risk of cardiovascular disease

This is not an original experiment but a narrative commentary and data synthesis. The authors reviewed existing literature on how quarantine (specifically COVID-19 lockdowns) altered two lifestyle factors — diet and physical activity — and linked those changes to cardiovascular disease (CVD) risk. They also examined the role of vitamin D in immune function against COVID-19 and the potential of home-based physical activity interventions.

The "intervention" being studied is quarantine itself (enforced or voluntary home confinement). The comparators are pre-quarantine lifestyle patterns. The outcome measures include:

Changes in dietary composition (fruit/vegetable intake, antioxidant/vitamin consumption)

Changes in physical activity levels (minutes per day, sedentary time)

Psychological stress and depression scores

Cardiovascular risk markers (inferred from diet and activity changes, not directly measured in this paper)

This paper does not report original data from a single study. Instead, it draws on multiple sources including:

Population-level surveys from Italy, China, and other COVID-affected countries during early 2020

General population samples (adults aged 18–65+ under quarantine orders)

No specific sample size is given; the commentary references studies ranging from small surveys (hundreds of participants) to national-level data

The authors are cardiologists and nutrition researchers from Italian universities (University of Modena and Reggio Emilia, University of Rome, University of Bologna). The paper was published in June 2020, during the first wave of the pandemic.

Since this is a commentary, there is no single measurement protocol. The authors cite studies that used:

Self-reported dietary recall questionnaires (e.g., 24-hour recall, food frequency questionnaires)

International Physical Activity Questionnaire (IPAQ) — short form, measuring MET-minutes per week

Psychological scales: Hospital Anxiety and Depression Scale (HADS), Perceived Stress Scale (PSS)

Blood biomarkers from other studies: serum 25-hydroxyvitamin D levels (for vitamin D status)

National sales data for food categories (e.g., increased sales of processed foods, decreased fresh produce)

The authors do not report specific cut-off scores or validation statistics for these instruments.

**Study design:** This is a narrative commentary/opinion piece, not a systematic review or meta-analysis. The authors selected studies they considered relevant, without a pre-registered search protocol, explicit inclusion/exclusion criteria, or formal quality assessment of the cited evidence.

**What the design can prove:** Very little on its own. A commentary can highlight emerging patterns, generate hypotheses, and synthesise expert opinion. It can point to plausible mechanisms (e.g., stress → comfort eating → weight gain → CVD risk).

**What the design cannot prove:** Causality. Without a controlled experiment, you cannot determine whether quarantine *caused* the observed changes, or whether other factors (seasonal effects, economic disruption, media exposure) were responsible. The paper cannot quantify effect sizes reliably, because it cherry-picks supporting evidence.

**Major methodological weaknesses:**

No systematic search strategy — the authors may have missed contradictory evidence

No statistical synthesis (no meta-analysis)

No assessment of publication bias

The paper is essentially expert opinion, albeit from domain experts

Temporal confounding: lockdowns coincided with spring in the Northern Hemisphere, when vitamin D levels naturally rise from sun exposure, yet the paper focuses on deficiency

No control group: everyone was under quarantine, so there is no counterfactual

**Why this matters for self-experimenters:** A commentary like this is useful for identifying *what to test* in your own n=1 experiment, but you should not treat its conclusions as proven facts. The real value is in the practical suggestions: home-based exercise, vitamin D monitoring, and dietary tracking.

Because this is a commentary, the "findings" are the authors' synthesis of other studies. Here are the specific claims they make, with the numbers they report:

**Dietary changes during quarantine:**

Reduced intake of fruits and vegetables: "a diet poor in fruit and vegetables is frequent during isolation" — no specific percentage given

Increased consumption of processed foods, sugary snacks, and alcohol — cited from Italian survey data showing a 30–50% increase in sales of comfort foods during lockdown

Low intake of antioxidants and vitamins, particularly vitamin D, vitamin C, and zinc

Vitamin D deficiency prevalence: the authors note that "some reports suggest that Vitamin D could exert a protective effect on such infection" — they cite a study showing that countries with higher COVID-19 mortality rates (Italy, Spain) also had higher rates of vitamin D deficiency (prevalence ~60–80% in elderly populations)

**Physical activity changes:**

"Reduced physical activity" — no specific MET-minutes or step-count data provided

Increased sedentary time: the authors reference WHO guidance that adults should do at least 150 minutes of moderate-intensity activity per week, and note that quarantine made this difficult

Home-based exercise strategies: the paper recommends bodyweight exercises, yoga, and online fitness classes, but provides no data on adherence or effectiveness

**Psychological effects:**

Quarantine is "associated with stress and depression" — no specific prevalence rates or effect sizes

The authors link stress to unhealthy eating patterns (emotional eating) and reduced motivation for physical activity

**Cardiovascular risk:**

The paper argues that the combination of poor diet, reduced activity, and stress increases CVD risk through multiple mechanisms: weight gain, insulin resistance, hypertension, dyslipidaemia, and systemic inflammation

No direct measurement of CVD events or biomarkers is reported

**Vitamin D and COVID-19:**

The authors claim that vitamin D "could exert a protective effect" on COVID-19 infection, citing observational studies showing lower vitamin D levels in severe cases

They do not report any randomised controlled trial data (none existed at the time of publication)

The paper does not provide effect sizes. However, based on the studies they cite and general population data:

**Diet shift:** A typical Mediterranean diet (common in Italy) provides ~400–600 mg/day of antioxidants (vitamin C, vitamin E, polyphenols). Quarantine may have reduced this by 30–50%, based on reduced fresh produce intake.

**Physical activity drop:** Pre-quarantine, average Italian adults reported ~200–300 minutes/week of total physical activity (including walking, work, leisure). During lockdown, this likely fell to <50 minutes/week for many, based on comparable studies from China and Spain.

**Vitamin D:** Serum levels typically drop by 10–20 nmol/L during winter months. Quarantine may have exacerbated this by reducing outdoor sun exposure. Deficiency (<50 nmol/L) affects ~40% of European adults in winter.

**CVD risk:** A 30% reduction in physical activity is associated with a ~15–20% increase in cardiovascular mortality over 5–10 years, based on large cohort studies (not cited in this paper).

For your own experiment: a meaningful change would be a 20% shift in any of these metrics (e.g., 30 fewer minutes of walking per day, or a 200-calorie increase in processed food intake).

**What the authors acknowledge:**

The paper is a "commentary" and "briefly analyzes" the situation — they do not claim systematic review status

They note that data are preliminary and that long-term effects are unknown

They call for "global action" but provide no specific policy recommendations

**What a critical reader would note:**

**No original data:** This is an opinion piece, not a study. It cannot be used to draw causal conclusions.

**Cherry-picked evidence:** The authors cite studies that support their narrative (e.g., vitamin D benefits) but do not discuss contradictory evidence (e.g., trials showing no benefit of vitamin D supplementation for respiratory infections).

**Confounding factors:** Quarantine effects are conflated with seasonal effects (spring), economic stress (job loss), and media-induced anxiety. You cannot isolate quarantine as the cause.

**Population specificity:** The paper focuses on Italian and European populations. Dietary patterns, vitamin D status, and physical activity norms differ dramatically by region. Findings may not generalise to other cultures.

**No dose-response data:** The paper does not specify how much diet or activity change is needed to increase CVD risk. "Unhealthy diet" is not quantified.

**Industry funding:** Not declared, but the authors are academic clinicians. No obvious conflicts, but the vitamin D claim aligns with supplement industry interests.

**Publication date:** June 2020 — very early in the pandemic. Subsequent research has both supported and contradicted these claims. For example, later large-scale studies found that vitamin D supplementation did not reduce COVID-19 severity in randomised trials.

**No blinding or randomisation:** Obviously impossible for a commentary, but the lack of systematic methodology means the conclusions are the authors' subjective interpretation.

For someone running their own n=1 experiment to test whether quarantine (or any period of home confinement) affects your diet, activity, and cardiovascular risk:

### What to test

**Primary intervention:** A structured home-based exercise program (e.g., 30 minutes of bodyweight exercises or yoga, 5 days per week) combined with a daily fruit/vegetable target (e.g., 5 servings per day)

**Comparator:** Your normal routine (no structured exercise, no dietary target) — use a 2-week baseline period before starting the intervention

**Dose:** 30 minutes of moderate-intensity exercise (heart rate 120–140 bpm for most adults) + 5 servings of fruits/vegetables daily

### Minimum meaningful duration

**Baseline phase:** 14 days (to establish your normal patterns)

**Intervention phase:** 21 days (3 weeks is the minimum to see measurable changes in biomarkers like blood pressure or fasting glucose)

**Total experiment:** 5 weeks minimum. For cardiovascular risk markers (e.g., LDL cholesterol), 8–12 weeks is better.

### What to measure (specific metrics)

**Physical activity:** Daily step count (use a phone or wearable), plus minutes of intentional exercise. Record in a log. Aim for ≥7,000 steps/day as a minimum target.

**Diet:** Daily servings of fruits and vegetables (1 serving = 1 cup raw or ½ cup cooked). Also track servings of processed foods (chips, cookies, fast food). Use a simple app or paper log.

**Body weight:** Weigh yourself at the same time each morning, after voiding, before eating. Weekly averages are more reliable than daily fluctuations.

**Blood pressure:** If you have a home monitor, measure at the same time each day (morning, before breakfast, after sitting 5 minutes). Systolic BP >130 mmHg is a red flag.

**Mood:** Use a 1–10 scale for stress and energy levels each evening. Or use the validated Perceived Stress Scale (PSS-10, free online).

**Optional biomarker:** Fasting blood glucose or HbA1c (fingerstick test, available at pharmacies). A change of >5 mg/dL is meaningful.

### Key confounds to control for

**Seasonal effects:** If you run this experiment in winter vs. summer, sunlight exposure and vitamin D levels will differ. Run the baseline and intervention in the same season, or measure vitamin D (blood test) at start and end.

**Sleep:** Poor sleep increases cravings for high-calorie foods and reduces exercise motivation. Track sleep duration and quality (e.g., 7–9 hours per night). If sleep changes, it's a confound.

**Stress events:** Major life events (work deadlines, relationship issues) will affect diet and activity. Note them in your log. If a major stressor occurs, consider extending the experiment.

**Alcohol intake:** Alcohol is a source of empty calories and reduces exercise recovery. Track drinks per day. Keep consistent between baseline and intervention.

**Medication changes:** Any new medications (especially blood pressure or cholesterol drugs) will confound results. Do not change medications during the experiment without consulting your doctor.

**Social support:** If you exercise with a partner during the intervention but not during baseline, the social component (not the exercise itself) could drive changes. Keep social context consistent.

### What a positive result would look like

**Physical activity:** Step count increases by ≥2,000 steps/day (e.g., from 4,000 to 6,000). Exercise minutes increase by ≥20 minutes/day.

**Diet:** Fruit/vegetable intake increases by ≥2 servings/day (e.g., from 2 to 4 servings). Processed food intake decreases by ≥1 serving/day.

**Body weight:** Loss of 0.5–1 kg (1–2 lbs) over 3 weeks, assuming no other changes. This corresponds to a ~500-calorie daily deficit.

**Blood pressure:** Systolic BP drops by 5–10 mmHg. Diastolic drops by 3–5 mmHg. This is clinically meaningful and reduces CVD risk by ~10–20%.

**Mood:** Stress score decreases by ≥2 points (on 1–10 scale). Energy score increases by ≥2 points.

**Optional biomarker:** Fasting glucose drops by 5–10 mg/dL. HbA1c drops by 0.2–0.5% (if elevated at baseline).

**What to do if results are negative:** If you see no change after 3 weeks, check your adherence (were you actually doing the exercise? eating the vegetables?). Extend the intervention to 6 weeks. Some changes (e.g., cholesterol) take longer. Also check for confounds: were you sick? sleeping poorly? under unusual stress? If adherence was good and confounds were controlled, consider that the intervention dose may be too low (e.g., 30 minutes of exercise may not be enough for you — try 45 minutes).

**Bottom line for self-experimenters:** This commentary highlights plausible mechanisms linking quarantine to CVD risk, but it is not evidence that these effects are universal or large. Your own experiment will tell you whether *you* respond to home confinement with diet/activity changes, and whether a structured intervention reverses them. Use the specific metrics above, control for confounds, and run for at least 5 weeks total. A positive result would be a 10–20% improvement in diet quality, activity level, or blood pressure — enough to meaningfully reduce your cardiovascular risk.