How Nutritional Deficiencies Develop
Nutritional deficiencies do not occur spontaneously but usually develop due to one or more reasons and evolve over time passing through a series of stages of increasing severity.
The sequence of their evolution was best described in the 1960s by the late Professor Myron Brin when he induced experimental vitamin B1–thiamin deficiency in a group of volunteers. Deficiency developed within a few weeks and he was able to observe it evolving through several distinct stages. Though no one became seriously ill during the experiment his observations lead to an understanding of how an individual can progress from a state of nutritional adequacy to serious ill-health and even death.
Brin M. Erythrocyte as a biopsy tissue for functional evaluation of thiamine adequacy. J. Am. Med Ass. 1964: 187: 762-766
Stages in the Development of a Nutrient Deficiency
- Negative Balance
- Decline in Tissue Stores
- Loss of Function:
- Symptoms of Deficiency
- Signs of Deficiency
- Organ Failure
A clear and thorough understanding of this simple sequence is essential to clinical assessment of nutritional state and in particular the interpretation of laboratory tests of nutritional state.
The process of assessing the nutritional status of an individual is simply a matter of determining in which of these five categories they fall for each essential nutrient.
Important Clinical Messages in Nutrition Assessment
- A state of negative balance can develop for reasons other than just poor intake
This explains why the correlation coefficients between the intake of a nutrient and the blood level of the same nutrient are often very low especially in older people
- Mild deficiencies are much more prevalent than severe ones
Many doctors are only familiar with the clinical picture of severe deficiency and will easily overlook a mild deficiency
- The symptoms of nutritional deficiency precede the signs
Physical signs of deficiency are less prevalent than the symptoms of the deficiency
- A biochemically-diagnosed deficiency (which reflects a decline in tissue stores) will precede the development of a loss in tissue function
Not all “deficiencies” diagnosed by laboratory methods alone result in a loss of function
- Death is the terminal consequence of some deficiencies
It is likely that a significant percentage of deaths in the UK are preceded by treatable nutritional deficiencies. The merits of treating/preventing them have yet to be broadly explored.
Why Do Nutritional Deficiencies Develop
Deficiencies develop for a reason and all the reasons fall into one of five categories of causes that result in a state of negative nutrient balance.
Causes of a State of Negative Balance
- Inadequate Intake
- Poor Absorption
- Increased Requirement
- Increased Losses
- Altered Metabolism
There are a variety of reasons for each of these possible causes.
Causes of a State of Negative Balance
- Inadequate Intake - Poor food supply, poor food choices, feeding or swallowing difficulties
- Poor Absorption - Coeliac disease, inflammatory bowel disease, alcohol excess and dietary tannins,
- Increased Requirement - Growth, pregnancy and lactation, many chronic illnesses and recovery from weight loss
- Increased Losses - Renal disease, poorly controlled diabetes, burns and widespread skin disease
- Altered Metabolism -Alcohol excess, drugs, disease, environmental pollution and genetic variations in metabolism
The known medical and non-medical risk factors for the development of a nutritional deficiency will exert their influence through one or more of the five possible causes
Other Factors That Influence the Clinical Recognition of Nutritional Deficiencies
Other factors may need to be borne in mind when assessing the presence and likely impact of risk factors for the development of a nutritional deficiency:
- Time scale - The time taken for a nutritional deficiency to develop in an individual who was previously adequate varies enormously from a few weeks in the case of vitamin B1–thiamin to decades in the case of calcium
- Population distribution - When dealing with populations in which severe deficiencies are not commonplace there is likely to be a decreasing proportion of the population that can be assigned to the categories progressing from adequacy to death.
For example, in British women of child-bearing age: % have an intake below the LRNI, many but not all of these are likely to have symptoms (fatigue and irritability), but only % have anaemia (mild organ failure) and very few if any are dying as a result of anaemia.
- Symptoms versus signs -
In the development of a deficiency, because symptoms precede the development of signs, there are usually many more people with symptoms of a deficiency than there are with signs of one.
Additionally those with signs of a nutritional deficiency should also have symptoms as well as an identifiable cause(s) for their deficiency.
- Not all “deficiencies” are clinically important -
An inadequate intake is usually defined as an intake below the Lower Reference Nutrient Intake, LRNI, “an amount that is enough for only the few people in a group that have low needs”
However it will be adequate for some (approximately 3% of the population) and some others may also adapt to a low intake without any significant health consequences especially if the remainder of their diet is healthy.