Why ‘normal’ isn't always optimal: how to get the most out of your results

Discover how to optimise a set of normal results to help you reach your real peak.

dr-joshua-smith

Author: Dr Joshua Smith - Clinical Insights Lead MBBS, BMedSci, PGCertMedEd

Reviewed by: Dr Tina Ghela – Digital Clinician, MBBS, MRCGP, BSc (Hons)

Published on: 16 September 2025

Here’s the truth: ‘normal’ doesn’t always mean optimal. Most reference ranges are designed to flag disease. They’re based on population averages, not high performers. So, if you’re someone who’s looking for that extra edge — more energy, sharper focus, better recovery, long-term vitality — then it’s time to rethink your results.

In this blog, we’ll explore the difference between normal and optimal for key blood markers and how aiming higher could help you unlock the next level of your health.

This article covers:


What makes a result ‘normal’?


When you get a blood test, your results are compared against the ‘normal reference range’. This is a set of values that most healthy people are expected to fall within.

How are normal ranges calculated?

Labs collect blood test results from a large group of people, ideally those considered healthy, and plot them on a graph. Most people’s results cluster around the middle, with fewer people at the very low or very high ends. The ‘normal range’ is usually set to include the middle 95% of results. This means that the bottom and top 2.5% are considered ‘abnormal’ (even though these individuals may be perfectly healthy).

The problem with normal reference ranges

The 95% method doesn’t always account for how healthy the sample population is. There could be people in the sample who were unwell or at risk of disease, which skews the average. Secondly, these ranges reflect what’s most common, not what’s best for long-term health.

Ranges based on health outcomes

For some tests, things get more sophisticated. The normal range is set according to research linking specific levels to actual health risks or benefits. For example, the normal range for HbA1c (a measure of blood sugar levels) is based on studies showing that HbA1c above a certain threshold is linked to a higher risk of developing diabetes.


What are optimal ranges?


Optimal ranges represent the sweet spot where research shows you’re most likely to feel great, perform at your best, and reduce your risk of future health problems. These ranges are based on evidence linking specific levels to:

  • Lower risk of chronic diseases
  • Better energy and mental clarity
  • Enhanced physical performance
  • Improved longevity
  • Optimal body functioning

Reaching the ‘optimal’ range doesn’t guarantee perfect health — your wellbeing depends on many factors, from your lifestyle to your medical history, genetics, and unique circumstances.

But by keeping your biomarkers within the optimal ranges, you’re giving your body the best foundation to thrive.


Key biomarkers: normal vs optimal


Let’s dive into some of the most important biomarkers where the difference between normal and optimal can make a real impact on how you feel and function day-to-day.

Vitamin D

Normal: 50–250 nmol/L
Optimal: 75–125 nmol/L

Most vitamin D guidance focuses on bone health, but vitamin D also supports your immune system, heart, brain, mood, and may even prevent certain cancers [1].

The magic number? Most research shows that levels above 75 nmol/L tend to be best for your overall health [2]. The Endocrine Society suggests that some people might need at least 50 μg (2000 IU) per day to maintain these levels, and people with obesity often need more [3]. Don’t take more than 50 μg (4,000 IU) of vitamin D a day, unless advised by your doctor, as it could be harmful [4].

Benefits of optimal vitamin D levels:

  • Enhanced immune system function and reduced infection risk
  • Better mood and reduced risk of seasonal depression
  • Improved muscle strength and physical performance
  • Lower risk of cardiovascular disease
  • Better pregnancy outcomes
  • Reduced risk of certain cancers

Many people in the UK have suboptimal levels, especially during winter months, so it's worth considering a supplement. Unlike most nutrients, we get very little vitamin D from our diet.
 

How to optimise vitamin D

  1. Get outside when you can – A bit of sunshine on your skin helps your body make vitamin D. But from October to March, there usually isn’t enough in the UK, so this really only works in spring and summer.
  2. Eat vitamin D-rich foods – Try to include oily fish like salmon or sardines, egg yolks, red meat, and foods with added vitamin D (check the labels on cereals and spreads). But realistically, most people won’t get enough from food alone.
  3. Consider a supplement – The simplest way to keep your vitamin D at an optimal level is with a daily supplement. Most adults do well with 10–50 μg (400–2,000 IU), but people with obesity often need a bit more. If you’re unsure, talk to your doctor or pharmacist.
  4. Check your levels – It’s a good idea to check your vitamin D with a blood test if you’re taking higher doses. This makes sure you’re not taking too much.


Ferritin

Normal: 30–300 μg/L (varies by age and gender)
Optimal: 70–100 μg/L for most adults

Ferritin is a measure of your iron reserves. If your ferritin is low, you’re more likely to feel tired, and you may even see changes in your skin, hair, and nails.

Most doctors say a ferritin level over 30 μg/L is enough to rule out iron deficiency. But if you’re looking to optimise your performance and hair health, you might want to aim a bit higher. One study showed that keeping levels over 50 μg/L might be good for sleep [5]. And when it comes to hair health, most experts tend to advise keeping levels at 70  μg/L and above [6].  

Ferritin can go up if you have inflammation or certain conditions like obesity, diabetes, or arthritis, even if your iron stores are low. If you have one of these, a ferritin level over 100 usually means you’re not lacking iron [7]. 

Benefits of optimal ferritin levels:

  • Better energy levels throughout the day
  • Better exercise performance and recovery
  • Improved focus
  • Stronger hair and healthier skin and nails
  • Better sleep quality

How to optimise ferritin

  1. Eat iron-rich foods – Try to include red meat, liver, and shellfish like mussels or clams, which are great sources of easily absorbed iron. If you’re vegetarian or vegan, beans, lentils, tofu, spinach, pumpkin seeds, and fortified cereals can help, though your body doesn’t absorb iron from plants as easily. 
  2. Pair plant foods with vitamin C – Eating vitamin C-rich foods (like oranges, strawberries, peppers, or broccoli) with iron-rich meals helps your body absorb more iron from plants. 
  3. Consider an iron supplement – If your ferritin is low or you struggle to get enough iron from food, your doctor or pharmacist may recommend a supplement. Always check your iron level before starting supplements, as too much iron can be harmful.


High-sensitivity CRP (hs-CRP)

Normal: <3 mg/L
Optimal: <1 mg/L

Hs-CRP measures inflammation in your body. While levels under 3 mg/L are considered normal, research consistently shows that levels under 1 mg/L are associated with the best health outcomes [8]. 

Why does it matter? Even low-level, ‘silent’ inflammation (that you can’t see or feel) is now thought to play a key role in the development of heart disease and stroke. That’s why keeping your hs-CRP as low as possible is linked to the best cardiovascular health. 

Benefits of optimal hs-CRP levels:

  • Lower risk of heart disease, heart attack, and stroke
  • May reduce risk of diabetes, metabolic syndrome, and some cancers
  • May lower risk of other age-related diseases

Many people have higher hs-CRP due to factors like excess weight, a diet high in processed foods, inactivity, poor sleep, or long-term stress. Certain conditions, like autoimmune diseases or infections, can also raise hs-CRP.  

Just under half of Medichecks customers have suboptimal hs-CRP levels, which may be increasing their risk of heart disease.  

How to optimise hs-CRP

  1. Eat an anti-inflammatory diet – Aim for plenty of fruit and vegetables, whole grains, oily fish (like salmon or mackerel), nuts, seeds, and healthy fats such as olive oil. Try to cut back on processed foods, sugary snacks, and red or processed meats. 
  2. Exercise regularly – Even a brisk walk most days of the week can help bring inflammation down. 
  3. Maintain a healthy weight – Carrying extra weight, especially around your waist, can raise hs-CRP. Small changes can make a real difference. 
  4. Prioritise sleep and stress management – Lack of sleep and chronic stress can raise hs-CRP. Good sleep habits and regular relaxation (like mindfulness, hobbies, or time outdoors) really do help. 
  5. Manage other health conditions – Keeping things like high blood pressure, diabetes, or autoimmune conditions under control with your doctor’s help can also help keep hs-CRP low. 


Active B12

Normal: >35 pmol/L
Optimal: >70 pmol/L

Active B12 measures the amount of vitamin B12 in your blood that your body can actually use. B12 is essential for energy, brain health, mood, and healthy nerves and blood cells. 

Labs usually say that anything above 35 pmol/L is ‘normal’, but levels over 70 pmol/L are more reassuring. Levels in the ‘low-normal’ range (35–70 pmol/L) don’t always rule out a true B12 deficiency, especially if you have symptoms [9]. In these cases, a methylmalonic acid (MMA) blood test is often recommended. A high MMA result can confirm a B12 deficiency, even if your B12 appears normal. 

Around one in five customers has suboptimal active B12 levels.

Benefits of optimal B12 levels:

  • More stable energy
  • Sharper memory and focus
  • Healthier mood
  • Better nerve health and red blood cell production

B12 deficiency can develop slowly over years, and symptoms can be subtle until levels become severely low. This is particularly important for vegetarians, vegans, and older adults. 

How to optimise B12

  1. Eat B12-rich foods – Best sources are animal products: meat, fish, eggs, and dairy. If you’re vegetarian or vegan, fortified foods (such as plant milks and cereals) or a B12 supplement are usually needed. 
  2. Consider a supplement – If your B12 is low, you have symptoms, or you follow a plant-based diet, a daily supplement is a safe and effective option. 
  3. Check your levels if you’re at risk – Older adults, people with gut problems (like coeliac or Crohn’s), or people taking certain medications (e.g., metformin, PPIs) may be more likely to run low on B12. 
  4. Test again if unsure – If your active B12 is in the low-normal range (below 70 pmol/L), especially with symptoms, ask your doctor about further tests like MMA. 


Magnesium

Normal: 0.7–1.0 mmol/L
Optimal: 0.85–1.0 mmol/L

Magnesium is a vital mineral for your muscles, nerves, heart, and bones; but its benefits don’t stop there. It also plays a big part in keeping your energy steady, supporting restful sleep, helping you handle stress, and keeping your blood sugar in check. 

Although most labs set the lower limit for magnesium at 0.7 mmol/L, blood tests can sometimes miss a hidden deficiency, especially if your result is only just in the ‘normal’ range. That’s why aiming for at least 0.85 mmol/L is often recommended, as it gives extra reassurance you’re not running low [10]. 

If you’re not getting enough magnesium, you might feel more tired, notice muscle cramps or twitches, struggle with headaches or sleep, or — if your levels drop a lot — have an irregular heartbeat.  

The problem is many of us aren’t getting enough from our diets. In fact, our own data shows that about one in six people has less-than-ideal magnesium levels.

Benefits of optimal magnesium levels: 

  • Likely improved sleep quality 
  • Reduced muscle soreness 
  • Improved performance and recovery 
  • Lower risk of heart rhythm problems 
  • May help with headaches and mood

How to optimise magnesium

  1. Eat magnesium-rich foods – Good sources include green leafy vegetables (spinach, kale), nuts and seeds (almonds, pumpkin seeds), whole grains, beans, lentils, and dark chocolate. 
  2. Consider a supplement – If you can’t get enough from food or your magnesium is low, a magnesium supplement may help. Always talk to a healthcare professional before starting high-dose supplements, as too much can cause diarrhoea or, rarely, more serious problems. 
  3. Limit excess alcohol and processed foods – These can make it harder for your body to absorb or keep enough magnesium. 
  4. Check your levels if you’re at risk – People with digestive issues (like Crohn’s or coeliac disease), type 2 diabetes, older adults, or those on certain medications (diuretics, PPIs) are more likely to be low in magnesium. Our Advanced Well Woman Blood Test and Advanced Well Man Blood Test include magnesium. 


Total testosterone (males)

Normal: 8–30 nmol/L
Optimal: 15–30 nmol/L

Testosterone is the main male sex hormone, but it’s not all about sex drive. It plays a crucial role in building muscle, keeping your bones strong, supporting your mood and energy, and even helping to maintain a healthy heart and brain. 

Testosterone levels naturally decline as you get older, usually dropping by about 1% per year after your 30s. However, some men experience lower levels earlier, which can leave you feeling unusually tired, less motivated, struggling with low mood, weaker muscles, more body fat, or a drop in libido. 

Most labs set the ‘normal’ range between 8 and 30 nmol/L, but symptoms of low testosterone often show up even when you’re within that range, especially in the lower end. Many experts consider levels of 15–30 nmol/L to be optimal for most healthy, younger to middle-aged men. 

Benefits of optimal testosterone levels: 

  • More energy and motivation 
  • Better mood and focus 
  • Stronger muscles and bones 
  • Healthier body composition (less fat, more lean mass) 
  • Improved sex drive and sexual function 
  • Better heart health and lower risk of metabolic syndrome

How to optimise testosterone

  1. Maintain a healthy weight – Carrying excess fat, especially around your waist, can lower testosterone. Even small reductions can make a difference. 
  2. Exercise regularly – Both strength training and cardio (especially HIIT) can help raise your testosterone naturally. 
  3. Get enough sleep – Poor sleep is a common but under-recognised cause of low testosterone. Aim for at least 7–8 hours a night. 
  4. Eat a balanced diet – Make sure you’re getting enough healthy fats, protein, and key nutrients (zinc, vitamin D, magnesium). 
  5. Limit alcohol and manage stress – High alcohol intake and chronic stress can drag your levels down. 
  6. Treat underlying conditions – Diabetes, sleep apnoea, and some medications can affect testosterone. Addressing these can help. 


You can check your testosterone levels easily from home, and if treatment is appropriate, the team at Leger are specialists in testosterone replacement.


Key takeaways


Reaching the normal range is a great start, but aiming for optimal levels gives you the best chance of feeling and performing at your best. Simple lifestyle changes — diet, movement, sleep, smart supplementation — can help you move from ‘OK’ to ‘optimal’. If you’re curious where you stand, consider a broad health check such as our Advanced Well Woman Blood Test or Advanced Well Man Blood Test.
 


References

  1. Vitamin D deficiency - PubMed. [cited 26 Aug 2025]. Available: https://pubmed.ncbi.nlm.nih.gov/17634462/ 
  2. Lugg ST, Howells PA, Thickett DR. Optimal Vitamin D Supplementation Levels for Cardiovascular Disease Protection. Dis Markers. 2015;2015: 864370. doi:10.1155/2015/864370 
  3. Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96: 1911–1930. doi:10.1210/jc.2011-0385 
  4. Vitamin D. In: nhs.uk [Internet]. 23 Oct 2017 [cited 28 Aug 2025]. Available: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/ 
  5. Smith S, White J, Jambhekar S. 0717 Restless sleep associated with low ferritin levels: A Retrospective Study in a Pediatric Sleep Center. Sleep. 2023;46: A314–A315. doi:10.1093/sleep/zsad077.0717 
  6. Aslam MF, Khalid M, Amad Aslam M. The Association of Serum Ferritin Levels With Non-scarring Alopecia in Women. Cureus. 14: e32123. doi:10.7759/cureus.32123 
  7. Garg N, Kotru M, Yadav A, Rusia U, Sikka M, Kalra OP. Serum ferritin <70 μg/L predicts functional iron deficiency in patients with chronic kidney disease. Saudi J Kidney Dis Transpl. 2018;29: 1035–1041. doi:10.4103/1319-2442.243956 
  8. Bassuk SS, Rifai N, Ridker PM. High-sensitivity C-reactive protein: clinical importance. Curr Probl Cardiol. 2004;29: 439–493.  
  9. Interpreting investigation results | Diagnosis | Anaemia - B12 and folate deficiency | CKS | NICE. [cited 29 Aug 2025]. Available: https://cks.nice.org.uk/topics/anaemia-b12-folate-deficiency/diagnosis/interpreting-investigation-results/ 
  10. Rosanoff A, West C, Elin RJ, Micke O, Baniasadi S, Barbagallo M, et al. Recommendation on an updated standardization of serum magnesium reference ranges. Eur J Nutr. 2022;61: 3697–3706. doi:10.1007/s00394-022-02916-w 
  11. Grant WB, Wimalawansa SJ, Pludowski P, Cheng RZ. Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines. Nutrients. 2025;17: 277. doi:10.3390/nu17020277