In my 30s and my energy is not what it was. Why?

Studies show that the body changes only slowly in the 30s. A US study that followed healthy adults found that peak aerobic capacity fell by 3% to 6% per 10 years in people in their 20s and 30s, a much smaller drop than in later decades, whatever their exercise habits. England's NHS, in its self-help tips for tiredness, says many cases of tiredness are due to stress, not enough sleep, poor diet and other lifestyle factors. In Thailand's 2015 time-use survey, 58.3% of people aged 30 to 39 slept within the recommended 7 to 9 hours, and 48.0% broke up sitting at least every 2 hours. Look at sleep, sitting, activity and stress alongside each other: aim for 7 or more hours of sleep, get up from your seat at least every 2 hours, stay active and do strength work on 2 or more days a week. If you have felt tired for a few weeks without knowing why, see a doctor.

Does the body really slow down in your 30s?

Fitness changes slowly at first

Peak aerobic capacity is a measure of how much oxygen your body can use at its hardest effort, and it is one way researchers track fitness with age. Fleg and colleagues at the US National Institutes of Health measured it repeatedly in healthy adults over a median of 7.9 years. They found a decline in every decade, in both men and women and whatever their leisure-time exercise habits, but its speed changed a lot with age:

The study was done in the United States in people without known heart problems, so it shows a general pattern rather than what will happen to any one person.

Muscle mostly holds through the 30s

Janssen and colleagues measured skeletal muscle with whole-body scans in 468 men and women aged 18 to 88. Muscle as a share of body weight began to fall from the 20s, but a noticeable drop in the actual amount of muscle was not seen until the end of the 40s, and it was mainly in the lower body. The study compared people of different ages at one point in time rather than following the same people, so it does not show how any one person's muscle changes.

What this means for how you feel

These studies measured fitness and muscle, not how tired people felt. For tiredness, the NHS says many cases are due to stress, not enough sleep, poor diet and other lifestyle factors. So it makes sense to look at sleep, sitting, activity and the load from work and family alongside each other, and to see a doctor if tiredness goes on for a few weeks without a clear reason.

How do Thai people in their 30s spend their day?

What Thai national surveys found

What these numbers can and cannot tell us

All three surveys asked people to report their own time, which is easy to over- or under-estimate. The time-use figures are from 2015, and the 2021 survey took place during the pandemic, when many people worked from home. The surveys show how people spend their day, not why they feel tired. In the 2015 survey, people aged 30 to 39 were more likely than those aged 18 to 29 to meet each guideline, so the 30s do not look worse than the 20s in these data. Still, about 4 in 5 people in their 30s reached the activity level, while only about half slept within 7 to 9 hours or broke up sitting. Sleeping outside 7 to 9 hours includes both sleeping less than 7 hours and more than 9; the study does not split the two. In the separate 2021 survey of all ages, most activity came from work.

Activity at work is not the same as exercise

In the 2021 survey, more than 80% of all activity came from work. People with higher education and income, and those living in Bangkok and the Central region, were more likely to sit for long hours. If your work moved from on your feet to a desk in your late 20s or 30s, your day may have become much less active without you noticing.

What else can make me feel more tired in my 30s?

England's NHS lists common causes of tiredness and fatigue. The right-hand column gives this article's own examples of how they can show up:

For a fuller look at causes, see Tired, drained and sleepy all day: what causes it? If long hours are the main issue, see Working over 48 hours a week: how can I look after myself?, and if it is a young child, see Worn out from parenting and it keeps piling up. What helps?

How much sleep and movement should I aim for?

Liangruenrom and colleagues note that Thailand was the first country to release 24-hour movement guidelines for adults, which look at activity, sitting and sleep together across the whole day. Because the day has only 24 hours, time spent sitting or on screens late at night comes out of the time left for sleep or movement.

Where can I start this week?

Sleep

• Keep the same bed and wake times on most days. The NHS advises going to bed and getting up at the same time every day and taking time to relax before bed.
• Keep caffeine out of the evening. The NHS says the effects of caffeine can last up to 7 hours.
• Cut down on alcohol before bed. The NHS notes that you sleep less deeply after drinking.

Sitting and moving

• Stand up and move at least every 2 hours at work, in line with the Thai guidelines. Setting a reminder helps.
• Add a brisk walk at lunch or on the way home. The NHS suggests starting with a small amount of exercise and building up gradually over weeks and months towards 2 hours 30 minutes of moderate activity a week.
• Do two short muscle-strengthening sessions a week that work the major muscle groups, as the WHO guidelines advise. Exercises using your own body weight need no equipment.

For ideas on breaking up a desk day, see I sit at work all day and barely exercise. Where do I start? If you feel worn out after starting, see Still tired the day after exercise. How do I recover?

Meals and stress

• The NHS suggests eating regular meals and healthy snacks every 3 to 4 hours rather than a large meal less often.
• Build in something relaxing each day, such as exercise, music, reading or time with friends, which the NHS lists as ways to manage stress.

When should I see a doctor about feeling tired?

The NHS advises seeing a doctor if:

• you have been feeling tired for a few weeks and are not sure why
• your tiredness affects your daily life
• you feel tired and have other symptoms, such as weight loss or mood changes
• you have been told you make gasping, snorting or choking noises when you are asleep

The NHS also advises not to diagnose yourself from symptoms but to see a doctor if you are worried. Tell the doctor about any medicines and health products you use. If tiredness comes with low mood or worry that does not lift, talk to a doctor; in Thailand, you can call the Department of Mental Health's 1323 mental health hotline.