Risk factors are one of the key concepts within epidemiology, the study of the distribution and determinants of diseases and health-related events or states. Risk factors and causes form the 'determinants' part of epidemiology. Diseases and health issues stem from a complex interplay of several different factors. A risk factor is any one of these variables which correlates to an increased risk of a disease or health condition occurring.
Risk Factor Definition
Risk Factors are any variables that correlate to an increased risk of a disease, other health-related event, or state occurring. Risk factors can relate to lifestyle choices, your environment or other uncontrolled characteristics.
Some risk factors may be controlled by individuals, and others may not. There are four important non-controllable risk factors that cannot be determined by us. These are our:
Any risk factor that does not fit into these categories can be controlled. Some examples of these are chemical exposure, diet, exercise level and BMI.
BMI - Body mass index is a value with the units kg/m2, derived from a person's weight in kg and height in metres. It is used to categorise people into underweight, normal weight, overweight, moderately obese and severely obese and very severely obese. It is, however, a flawed measurement as it operates solely based on mass and height, meaning it may give flawed results in cases such as unusually short individuals or those with high muscle mass.
Fig. 1 - The four uncontrollable risk factors, age, gender, race and family history
List of Risk Factors Classes
Fig. 2 - Examples of each of the six categories of risk factors
Risk factors may be split into six different categories, which are shown below, with some examples of each attached:
- Biological
- Elevated blood sugar
- Elevated blood pressure
- Excessive cholesterol
- Chemical
- Carcinogens
- Mutagens
- Neurotoxins
- Physical
- Posture
- Temperature
- Humidity
- Psychosocial
- Excessive workloads
- Lack of control over own workload
- Restrictive timelines
- Personal
- Physical inactivity
- Diet and nutrition
- Excessive unprotected exposure to the sun
- Others
Correlation Does Not Imply Causation
When discussing risk factors, and any concept in science in general, we must be careful with how we use words like correlation and causation. Causation means that one thing directly causes another. An example of this would be saying that smoking causes lung cancer. This is incorrect, as many people smoke for decades and never develop lung cancer. This means that smoking is not a direct cause of lung cancer, but it's a hugely significant and big risk factor!
Fig. 3 - A simple illustration of the difference between correlation and causation
Correlation - A link between the values of one or more variables, without a change in one necessarily being the cause of changes in others.
Causation - A change in one variable causes a change in another.
Unless two variables have undergone empirical testing to confirm that a change in one causes a change in the other, while all other variables are controlled, we cannot confidently say that one thing causes another. Due to the complex nature of human health conditions and the ethical concerns of experimenting on humans, this causal nature is often incredibly hard to establish!
As such, we generally say that two things are correlated or display correlation. This means that there is some kind of link between two variables. However, one change does not necessarily cause a change in the other. We have to differentiate between causation and correlation because there are usually other factors at play that affect our health. There is very rarely only one cause for a particular disease. As we will discuss further in the article, lifestyle factors, genetic components, and environmental factors usually contribute to the development of a disease.
It's important to recognise, however, that some correlations are more than well established. For example, the adverse effects of smoking and alcohol on unborn babies and organ (liver and brain) function are undisputed.
Risk Factors for Diabetes
Generally, when one discusses risk factors of diabetes, they will be referring to type 2 diabetes as this is the kind of diabetes that is acquired, unlike type 1 diabetes which stems from an autoimmune attack on the insulin-producing cells of the pancreas.
Diabetes is a severe and prevalent disease. Learn more about the two types of this disease by reading our article Diabetes and check out the risk factors for each type in a brief overview below!
Type One Diabetes Risk Factors
The risk factors for type one diabetes are not as well known as type two diabetes. However, some of the known factors are family history and age.
- Family History - Having relatives with type one diabetes significantly increases the likelihood of an individual developing type one diabetes. This is likely due to genetic variations being a cause of type one diabetes.
- Age - Diabetes type one generally occurs in younger people, meaning that once you pass the young adult stage, you are much less likely to develop type one diabetes.
Type Two Diabetes Risk Factors
Unlike type one diabetes, the risk factors for type two diabetes are much more well known. These include prediabetes, obesity, age, family history, low activity, and race. Many of these risk factors can be changed with lifestyle changes, meaning that a healthier lifestyle can significantly decrease, but not eradicate, due to the non-causal nature of risk factors, the chance of someone developing type two diabetes!
- Prediabetes - Health condition where blood sugar levels remain above normal levels but are not high enough to be fully classed as type two diabetes. This is generally a sign of developing type two diabetes and is a significant risk factor.
- Obesity - A heightened BMI results in elevated levels of substances known to be linked to insulin resistance. This is shown by the linear increase in diabetes risk with BMI.
- Age - Increased age has been correlated with an increased risk of type two diabetes, as it most often occurs in those in middle age or older.
- Family History - Having relatives with type two diabetes also increases the likelihood of developing type two diabetes, meaning there may be some genetic element to diabetes type two.
- Low Activity - Exercise causes drops in blood sugar, weight and blood pressure, along with changing cholesterol levels. These all limit the chance of diabetes or its risk factors occurring, meaning low activity levels are a risk factor for type two diabetes.
- Race - Certain races and ethnicities exhibit higher incidences of type two diabetes, suggesting a heritable component to type two diabetes risk, like family history. Ethnicities at higher risk include those from black African, Afro-Caribbean and South East Asian backgrounds.
Risk Factors for Heart Disease
Heart disease, more properly termed cardiovascular disease (CVD), is the catch-all term for conditions which impact the heart and or blood vessels. This includes coronary heart disease, angina, hypertension, stroke and many others. Due to the large number of issues which come under the umbrella of CVD, there are a great many risk factors that increase the chance of developing any of the conditions described. These include but are not limited to high cholesterol, high blood pressure, diabetes, obesity, smoking and physical inactivity.
- High Cholesterol - Elevated cholesterol can lead to the formation of fatty plaques known as atheroma within the walls of arteries. This narrows them, meaning that sufficient blood cannot pass through.
- High Blood Pressure - This can cause damage to the inside of blood vessels, leading to bleeding or blockages, which then cause CVD.
- Diabetes - In a similar vein to high blood pressure, the high blood glucose levels in diabetes can cause damage to the blood vessels of the body. It may also damage the nerves which control the cardiovascular system.
- Obesity - Obesity raises cholesterol levels within the body, leading to more atheromas. It is also linked to an increased chance of diabetes and high blood pressure, meaning that lowering BMI significantly decreases the likelihood of CVD. In addition to these other knock-on effects, elevated BMIs also place the cardiovascular system under more stress.
- Smoking - Smoking can cause damage to the blood vessels of the body. It also places the cardiovascular system under additional stress and increases the chance of clot formation.
- Inactivity - A sedentary lifestyle increases the chance of all of these other risk factors, except smoking. This means that an increase in exercise significantly lowers the chance of CVD.
Coronary Heart Disease is one of the most known cardiovascular diseases and is often the precursor for other CVDs. Read more about it in our article on Coronary Heart Disease!
Risk Factors in Cancer
Cancer is a complex disease with many subtypes. The formation of cancer, termed carcinogenesis, is a complex process resulting from the breakdown of many systems.
Fig. 4 - An illustration of the multiple mutations needed for cancer to occur
Carcinogenesis is the formation of cancer through the transformation of healthy cells into cancer cells. Cancer cells are characterised by a rapid, uncontrolled proliferation.
The multi-hit hypothesis of cancer development states that several hits or mutations of genes are needed for cancer to form. Each of these mutations on its own generally would either be repaired or cause the cell to enter apoptosis.
- First, a mutation triggers the inactivation of tumour suppressing genes, which normally control the proliferation of cells. Suppose another mutation occurs which inactivates DNA repair mechanisms. In that case, this and future mutations can remain in the cell's genome without being removed.
Specific genes which can promote cell growth usually are active to a minimal degree. These genes are termed proto-oncogenes. If a mutation causes these genes' heightened activity, they are then called oncogenes.
- Further inactivation of tumour suppressor genes and the activation of proto-oncogenes eventually leads to the development of full-blown cancer within an organism.
An example of a critical tumour suppressor gene which is often inactivated is the p53 gene. This gene encodes a protein that activates DNA repair, halts the cell cycle to allow for repair, and triggers apoptosis if DNA damage cannot be repaired. Without this protein, the likelihood of a cell becoming cancerous increases significantly.
The risk factors for cancer are numerous, including age, family history, smoking, obesity, alcohol, viral infections, radiation exposure and exposure to chemicals such as carcinogens and mutagens.
- Age - The chances of developing cancer increases significantly with age simply because there has been more time for damage to occur.
- Family History - A family history of cancer increases your chance of developing the disease as it has a significant genetic component. This is illustrated by variant BRCA1 and BRCA2 genes. Certain alleles of these genes significantly increase the likelihood of breast cancer as they are involved in DNA repair, meaning mutant versions increase the likelihood of other mutations going unrepaired, leading to cancer.
- Smoking - Smoking has been linked to a 15-30x increase in the risk of lung cancer. Smoking cigarettes damages cells and the genetic material within, with cigarette smoke containing at least 70 carcinogens.
- Obesity - Obese individuals exhibit heightened hormone levels, which have been associated with an increased cancer incidence. Chronic inflammation stemming from obesity also increases oxidative stress on the body, increasing the likelihood of DNA damage. Fat cells also produce hormones, which directly encourage cellular proliferation. These are known as adipokines, and some also inhibit cancer formation. However, these are less prevalent in obese individuals.
- Alcohol - Alcohol gets broken down in the body into acetaldehyde, which is believed to be a carcinogen. It also creates reactive oxygen species, which cause oxidative stress, damaging genetic material. It may also impair the body's ability to process certain nutrients, which potentially protect the body from cancer, and increase the levels of hormones such as estrogen, which have also been linked to cancer.
As outlined above, there are multiple cancer risk factors. Mutagens, carcinogens and ionising radiation are all further examples of elements that can disrupt our genes and contribute to over proliferative cancerous cells from developing. Read more about the disease of our times in our Cancer article.!
Risk Factors - Key takeaways
A risk factor is a variable associated with an increased likelihood of a disease or health related event or state occurring.
Risk factors are correlations, not causes. We say risk factors are correlations, not causes, as it is generally difficult to empirically link a change in a variable to a change in a disease.
Cancer, CVD and diabetes all have their own risk factors, many of which overlap. These include genetic predisposition, age, obesity, low physical activity, ethnicity/race, high cholesterol, high blood pressure, diabetes, smoking, drinking, viral infection, radiation, carcinogen exposure and mutagen exposure.
References
- 10.1016/j.cmet.2021.12.012
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