How the body’s needs change over time: energy, protein and metabolism across the stages of life
Childhood and adolescence
During growth, the needs of energy y proteins are relatively higher per kilogram of body weight than in adulthood. The metabolism It is more active due to tissue growth and high spontaneous activity. Priority is usually given to protein quality (essential amino acids) and a regular distribution throughout the day to support the synthesis of new tissue. The specific figures depend on age, nutritional status and activity level.
- Energy: higher energy density per kg to support growth and maturation.
- Proteins: higher relative requirements per kg; the variety of high-quality sources is important.
- Metabolism: high expenditure due to growth and activity; considerable individual variation.
Adulthood and pregnancy/breastfeeding
In adulthood, the energy Daily energy requirements are determined primarily by body composition and physical activity. The proteins The aim is to maintain lean body mass and structural functions; spreading protein intake across meals helps to maximise its utilisation. During pregnancy and breastfeeding, energy and protein requirements tend to increase to support tissue growth and milk production, with requirements varying according to trimester, weight gain and clinical status.
- Energy: stable in adults of stable weight; gradual increases during pregnancy and breastfeeding, depending on the individual’s response.
- Proteins: intake and distribution throughout the day; relative increases during pregnancy and breastfeeding.
- Metabolism: the total expenditure depends on basal metabolic rate, the thermic effect of food and physical activity; physiological changes during pregnancy alter these factors.
Later adulthood
As we get older, the basal metabolic rate due to the loss of fat-free mass and hormonal changes, which may reduce the requirements for energy. However, the efficiency of using proteins Muscle synthesis may be reduced, which is why greater relative protein density and adequate amino acid quality are often prioritised. The metabolic response is variable and depends on comorbidities, medication and activity levels.
- Energy: often lower due to reduced energy expenditure at rest and, in some cases, reduced activity.
- Proteins: a relatively higher and well-distributed intake may be required to maintain muscle function.
- Metabolism: slowing associated with changes in body composition; there is considerable clinical variability.
Micronutrients that are typically required at different ages: calcium, vitamin D, iron and vitamin B12
In the case of the calcium and the vitamin D, requirements change with growth, sun exposure and bone health. Childhood and adolescence are key stages for achieving peak bone mass; during pregnancy and breastfeeding, requirements are adjusted due to physiological changes; and during the menopause and in old age, greater attention is paid to bone loss and reduced skin synthesis of vitamin D. Common sources of calcium include dairy products and fortified plant-based drinks, pulses, nuts and some vegetables; vitamin D comes from synthesis in the skin and from foods such as oily fish and fortified products. An excess of vitamin D can cause hypercalcaemia, so intake should be tailored to the individual.
The iron It is essential during periods of rapid growth (infancy, childhood, adolescence) and in women with heavy menstrual bleeding or during pregnancy. There may also be specific requirements in cases of prematurity, frequent blood donation or gastrointestinal blood loss. Bioavailability varies: haem iron (meat and fish) is absorbed more effectively than non-haem iron (pulses, whole grains, nuts), the absorption of which is enhanced by vitamin C and reduced by phytates, calcium or certain medicines. Supplementation without confirmation of a deficiency may mask underlying causes or lead to adverse effects.
The vitamin B12 It depends largely on intake and proper absorption. Groups at higher risk include older adults (due to hypochlorhydria or atrophic gastritis), people on restrictive vegan or vegetarian diets, infants whose mothers have a low intake of B12, and those taking medicines that interfere with its absorption (for example, metformin or proton pump inhibitors). It may take some time for their body’s reserves to be depleted, so a deficiency may go unnoticed. The main sources are foods of animal origin and fortified products; in diets lacking these foods, a planned intake is usually required.
Exercise and recovery as we age: changes in muscle mass and bone health to bear in mind
Changes in muscle mass and adaptation to exercise
With ageing, a reduction in muscle mass and function is common, linked to the sarcopenia, with atrophy of type II fibres, reduced neuromuscular recruitment and some anabolic resistance. To maintain functional capacity, it is often helpful to prioritise strength training Progressive and safe, with multi-joint movements, controlled ranges of motion and loads tailored to individual tolerance. Pushing close to technical fatigue without causing pain, combined with an adequate intake of protein and energy spread throughout the day, can promote recovery and the maintenance of function, particularly after demanding sessions.
Bone health and types of load
Bone remodelling slows down with age and the bone mineral density may decrease. Bone tissue responds to the mechanical load: weight-bearing exercises, strength training and impact exercises within tolerable limits can help to preserve bone architecture when properly tailored. Where there is a high risk of fracture, advanced osteoarthritis or prosthetic implants, the focus tends to be on gradual, low- to moderate-intensity loads, as well as exercises such as balance and proprioception which help to maintain stability. Nutritional status (protein, calcium, vitamin D) and moderate exposure to sunlight influence bone metabolism.
Recovery, risks and signs of adjustment
The recovery It tends to slow down over time due to changes in connective tissues, blood flow and the inflammatory response. It may be beneficial to space out intense sessions, alternate muscle groups and plan periods of lower load, adjusting the training load progressively. Signs such as residual fatigue, non-restorative sleep, morning stiffness or pain that limits activities suggest reducing volume or intensity and extending rest intervals. Longer warm-ups, mobility work and specific exercises targeting tendons and fascia help to manage discomfort associated with tendinopathies, bearing in mind that comorbidities and certain medications (for example, corticosteroids) may alter the response to exercise.
Sleep and circadian rhythms throughout life: why the amount of sleep needed may vary
The circadian rhythm and the homeostatic sleep pressure interact to determine when and how much we sleep. As the nervous system matures and we age, the synchronisation (phase), amplitude and stability of these rhythms change. The central biological clock, located in the suprachiasmatic nucleus, adjusts its response to light and social cues with age, whilst the the architecture of dreams (the NREM/REM ratio, continuity and depth) also changes, which explains variations in the number of hours of sleep required throughout a person’s life.
- Infants and young children: sleep is initially polyphasic, gradually becoming more consolidated at night; circadian rhythms are immature and gradually synchronise with light-dark cycles. The need for rest is greater and is spread over more periods.
- Childhood: sleep becomes more consistent throughout the night and naps tend to disappear, with a more robust and predictable circadian rhythm.
- Adolescence: this usually occurs delayed phase circadian rhythm (the body’s natural tendency to fall asleep and wake up later), which may clash with early academic timetables and reduce the total amount of rest.
- Adulthood: relative stability, with marked inter-individual differences characterised by the chronotype (morning or afternoon preference) and due to social demands.
- Advanced age: tendency to early stage (earlier sleep onset and wake-up time), reduced efficiency and increased fragmentation; deep sleep is often reduced, which may increase the perception of insufficient rest despite a similar amount of time spent in bed.
In addition to the stage of life, factors such as the genetics of the chronotype, exposure to natural and artificial light, regular sleep-wake patterns, the environment (noise, temperature), caffeine or alcohol consumption, comorbidities and medication, as well as shift work or changes in time zones. These variables can advance or delay the circadian phase and alter the continuity of sleep, meaning that sleep requirements are not uniform and can vary widely between individuals and at different stages of life.
Age-specific prevention: general and evidence-based clinical check-ups and recommended vaccinations
Childhood and adolescence
- Check-ups: monitoring growth and development, assessment of sight and hearing, oral health, and screening for mental health and substance use where appropriate.
- Risk-based screening: for anaemia, nutritional deficiencies or environmental exposures, depending on medical history and context.
- Vaccines: a systematic outline of the vaccination schedule (e.g. diphtheria-tetanus-pertussis, polio, Hib, pneumococcal, rotavirus, measles-rubella-mumps, chickenpox, hepatitis B), influenza annual, HPV in pre-adolescence/adolescence and recommendations regarding COVID-19 in accordance with the current guidelines.
Adults
- Health checks: blood pressure, weight/BMI and waist circumference; blood glucose and lipid profile at intervals tailored to individual risk; assessment of sexual health (STI screening in accordance with best practice and prevalence rates), mental health, and tobacco and alcohol use.
- Screened: cervical cancer including a smear test and/or HPV test at intervals recommended on the basis of age and medical history; a comprehensive cardiovascular assessment in the presence of risk factors.
- Vaccines: tetanus-diphtheria booster jabs (with a pertussis dose in adulthood), influenza annual, guidelines for dealing with COVID-19; consider hepatitis A and B, measles-rubella-mumps or chickenpox if there is no documented immunity, and meningococcal disease in the situations or groups indicated.
Older people
- Health checks: blood pressure, diabetes and dyslipidaemia; colorectal cancer screening from the age of 45–50, according to available guidelines and evidence; mammogram from the age of 40–50, in accordance with local guidelines; bone densitometry for women aged 65 and over (earlier if at risk) and for selected men; assessment of vision, hearing, frailty, falls and cognitive function; and a review of medication. In men with a history of smoking, an ultrasound scan for abdominal aortic aneurysm may be considered between the ages of 65 and 75, as indicated.
- Vaccines: pneumococcus from the age of 65, or earlier if there are risk factors; shingles from the age of 50–60, depending on the vaccine and availability; influenza annual; updated guidelines in light of COVID-19; tetanus-diphtheria and whooping cough booster jabs in accordance with the immunisation schedule; immunisation against VRS in certain older age groups, where indicated.
Age is a useful criterion for organising prevention by age group, but the indication, the start of treatment and the frequency of screened y vaccines These may vary by country, clinical history and risk level; decisions should be tailored to the individual, based on recognised guidelines and local availability.
