Harvard study highlights alcohol dangers and paths to recovery. Photo / Getty Images
The downsides to alcohol aren’t difficult to spot. The throbbing headache, churning stomach and racing heart we experience after one too many provides a not-too-subtle reminder that drinking really isn’t all that good for us.
Now, a major new review from Harvard has set out the true scale of the problem, linking alcohol to more than 60 diseases, from cancer and heart problems to type two diabetes and dementia.
But there is good news. One of the key findings of the review is that some of these alcohol-related harms – even ones accumulated across decades, as those first teenage tipples became a midlife Merlot habit – can be undone within weeks if you reduce your intake, or stop drinking entirely.
So what exactly can you reverse, and how long does it take?
If you’re a light or moderate drinker (that’s seven units/three 175ml glasses of wine per week, or 14 units/roughly seven glasses, respectively), then your alcohol intake isn’t necessarily causing damage to your heart, according to Sinclair Carr, a PhD candidate at Harvard and author of the review.
In fact, some research suggests this level of drinking may protect our heart health.
Two factors are thought to be to thank for this.
Alcohol leads to an increase in a hormone released by our body fat, adiponectin, which supports healthy blood sugar levels and reduces inflammation.
A tipple or two also lowers fibrinogen, a protein made in the liver; lowering it improves blood flow. In turn, this reduces the risk of heart disease and stroke.
However, moderate drinking can raise the risk of high blood pressure, while alcohol becomes especially risky for cardiovascular health when there is heavy single-session drinking (more than six units in a single session for women and eight for men) or routine heavy drinking (five units per day for women and 7.5 units per day for men).
“Binge drinking is associated with sudden cardiac events, even in people who don’t drink heavily on average – this is sometimes called ‘holiday heart syndrome’,” Carr notes.
This is when the heart temporarily beats chaotically (known as atrial fibrillation). It can cause blood to pool in the heart’s upper chambers, potentially leading to blood clots and stroke.
Regular heavy drinking can raise blood pressure, weaken the heart muscle (known as cardiomyopathy) and trigger an irregular heartbeat, he says.
There are a few reasons behind these effects on the heart. “There are direct toxic effects on heart muscle cells, increases in blood pressure and heart rate, disruption of the heart’s electrical conduction system, and effects on blood clotting and lipids,” Carr explains.
How to reverse the damage
Carr’s review found that some of these effects of heavy single-session drinking are reversible if you halve your intake or go teetotal.
One study revealed that moderate drinkers who had previously suffered from an irregular heartbeat reported fewer episodes when they quit alcohol for six months.
A separate piece of research found that when regular heavy drinkers halved their intake, their blood pressure fell by 5.5 mmHg systolic and 4 mmHg diastolic, in turn reducing their risk of a stroke and other heart complications.
“Most of the evidence on serious brain effects comes from heavy drinkers, often those diagnosed with alcohol use disorder,” says Dr Jurgen Rehm, a senior scientist at the Canadian Centre for Addiction and Mental Health, who co-wrote the review.
Heavy drinking causes the grey and white matter (tissue that makes up the brain) to shrink and increases the risk of dementia, he explains.
This is because of alcohol triggering inflammation in the brain and a thiamine deficiency. Also known as vitamin B1, thiamine is critical for brain cells to work properly, but alcohol hinders its absorption.
However, some worrying brain changes have also been detected from light or moderate drinking.
Research shows that drinking just seven units per week – the equivalent of three 175ml glasses of wine or three pints of 4% beer – shrinks the hippocampus (the brain’s memory processing centre) and speeds up memory decline.
How to reverse the damage
In heavy drinkers, some harms to the brain do appear to be reversible, Rehm notes, but you have to quit.
“Imaging studies suggest that cerebral atrophy (shrinking of brain tissue) may partly recover within weeks to months of stopping drinking, with measurable changes often appearing in the first few weeks,” he says.
“Cognitive functions such as attention, executive function and memory typically appear to improve within six to 12 months of abstinence in people with alcohol use disorder.”
However, some deficits in brain function may persist, especially among people who have been heavy drinkers for a long time, Rehm says. “Dementia risk does not appear to return fully to that of someone who never drank heavily.”
It’s not clear whether cutting back on alcohol is protective if you drink light or moderately, though this is likely the case. “It is genuinely hard to study, because people tend to only reduce or stop drinking when they get sick,” Rehm notes.
“Cancer risk increases from the first drink, with no safe threshold,” Rehm says.
Alcohol is classed as a Group one carcinogen by the International Agency for Research on Cancer, which means there is convincing evidence that it directly causes cancer, putting it in the same category as tobacco and asbestos.
“It increases the risk of cancers of the mouth, throat (pharynx and larynx), oesophagus, liver, colon and rectum, and female breast,” he adds.
“Emerging evidence also suggests that alcohol increases the risk of stomach, pancreas, and biliary tract cancers.”
This cancer-causing effect is thought to be because of how the liver processes alcohol: by producing an enzyme that converts alcohol to acetaldehyde, which is a highly toxic compound that damages DNA.
Acetaldehyde is also the driver of hangover symptoms, such as nausea and headache.
How to reverse the damage
Quitting alcohol is the only way to prevent it from causing cancer, Rehm says.
However, once DNA damage from alcohol has accumulated, it’s not possible to reverse this damage by reducing or stopping drinking.
“However, studies do suggest that reductions in drinking are associated with lower subsequent cancer risk,” he explains.
“Practical habits, such as having drink-free days, alternating with water or using smaller measures may help, but likely because they reduce how much someone drinks overall, which is what matters for cancer risk.”
Drinking alcohol is thought to drive up the risk of type two diabetes by worsening the body’s sensitivity to insulin and hindering the pancreas from releasing insulin to keep blood sugar stable.
“Heavy drinking also directly damages the pancreas, which contributes to diabetes risk,” Carr says.
However, the relationship between alcohol consumption and type two diabetes is more complicated than most other conditions.
“Observational studies find a lower risk of type two among people who have a low-to-moderate intake of alcohol, compared with no consumption, and higher risk at heavier intake,” he says.
The apparent benefit at low intake appears mainly in women, particularly those who are overweight or obese, but disappears in those who also drink heavily on occasion. “It’s not entirely clear whether this reflects a causal effect or is partly due to bias,” he notes.
How to reverse the damage
“Reversibility for diabetes specifically is less well studied, but reducing drinking can improve symptoms,” he says, such as blood sugar control and insulin sensitivity.
He adds that it is unclear whether reducing or stopping drinking will reverse established type two diabetes.
Despite low and moderate drinking habits being linked with a lower risk of type two in some groups, he doesn’t advise people to start drinking, or drink more, in an effort to reduce their risk.
“There are well-understood and effective ways to lower diabetes risk, such as weight management, diet and physical activity,” he says.
Alcohol is the sole cause of some gastrointestinal conditions, including certain sub-types of liver cirrhosis and pancreatitis, Rehm says, explaining: “Alcohol also appears to accelerate the progression of liver disease, even when it’s not caused by alcohol”.
This is because alcohol and acetaldehyde (the compound our bodies create to break down alcohol) are toxic to liver and pancreatic cells, as well as alcohol contributing to a build-up of fat, inflammation and scarring in the liver.
“While the risk of this happening increases strongly with heavy drinking, it is also elevated at lower levels of alcohol intake,” he says.
How to reverse the damage
“Reversibility here is mixed,” Rehm says. “Early-stage alcohol-related liver damage (fatty liver, even some fibrosis) appears to partly improve with abstention.”
However, advanced cirrhosis is generally considered not reversible, though reducing or stopping drinking may slow progression and reduce the risk of death, he adds.
“Acute pancreatitis episodes can resolve; chronic pancreatitis is generally considered not reversible, but again, stopping drinking is associated with fewer symptoms.”
Not all harms caused by alcohol can be undone.
Long-term heavy drinking can result in lasting damage to the immune system, cirrhosis and heart disease.
“The overall message is this: less alcohol is better for nearly every aspect of health, the harms are broad and serious,” Carr says.
“Some, but not all, appear to partly reverse when people reduce their drinking or stop.”
No specific alcohol is better or worse when it comes to health harms, he notes. While some studies have found that wine has health benefits, wine drinkers tend to be richer and have healthier diets, two factors that may be skewing results.
“It is worth noting that for cancer, the evidence does not support a safe threshold,” Rehm notes.
“Risk increases from the first drink. Whether to drink, and how much, is ultimately the individual’s decision. But people should make that decision with accurate information about the risks.”