Why Your Energy Dips After 40
If you feel like your energy has fallen off a cliff since turning 40, you are not imagining it. Several biological shifts converge during this decade that directly impact how much energy your body can produce and sustain throughout the day.
Declining CoQ10 production: Coenzyme Q10 is critical for mitochondrial energy production in every cell. Your body's natural production of CoQ10 peaks around age 20 and steadily declines with age, meaning your cells literally have less fuel to work with [1].
Changing hormones: Perimenopause often begins in a woman's early to mid-40s. Fluctuating estrogen and progesterone levels can cause fatigue directly and also disrupt the quality of your sleep, compounding the problem. For targeted menopause support, see our guide on supplements for menopause relief.
Sleep disruption: Hormonal changes, increased stress, and night sweats can fragment sleep. Poor sleep quality is one of the most common and most underestimated causes of daytime fatigue.
Nutrient absorption changes: As we age, our bodies become less efficient at absorbing key nutrients like B12, iron, and vitamin D. Even a well-balanced diet may not deliver the same nutritional value it did at 25.
The good news is that targeted supplementation can address many of these gaps. Here are four evidence-backed supplements that support sustained energy in women over 40.
1. CoQ10 (Ubiquinol)
CoQ10 is a coenzyme found in every cell in your body, concentrated in organs with the highest energy demands: the heart, liver, and kidneys. It plays a central role in the mitochondrial electron transport chain, which is how your cells generate ATP — the energy currency your body runs on.
After age 40, declining CoQ10 levels mean your mitochondria are working with a smaller supply of this essential cofactor. A 2018 review in Clinical Chemistry and Laboratory Medicine detailed how CoQ10 levels decrease with age and how this decline is associated with reduced cellular energy capacity [1]. A separate study published in Nutrition found that CoQ10 supplementation significantly reduced fatigue in healthy subjects [2].
Ubiquinol is the active, reduced form of CoQ10 and is more readily absorbed than the oxidized form (ubiquinone), making it the preferred choice for women over 40.
Suggested dose: 100–200 mg ubiquinol daily, taken with a meal containing fat for optimal absorption.
View Top-Rated CoQ10 on Amazon2. Iron + Vitamin B12
Fatigue is the hallmark symptom of anemia, and iron-deficiency anemia remains surprisingly common in women in their 40s — particularly those with heavy menstrual periods (a frequent occurrence during perimenopause) or those following plant-based diets.
Iron is essential for producing hemoglobin, the protein in red blood cells that carries oxygen to your tissues. Without adequate iron, your cells are essentially oxygen-starved, leading to persistent tiredness, brain fog, and weakness. The NIH Office of Dietary Supplements recommends 18 mg of iron daily for premenopausal women [3].
Vitamin B12 works alongside iron in red blood cell formation. B12 deficiency can cause a type of anemia that mirrors iron-deficiency symptoms. Absorption of B12 from food decreases with age due to reduced stomach acid production, making supplementation increasingly important after 40. The NIH notes that up to 15% of the general population may be B12 deficient [4].
Suggested dose: Iron 18–27 mg daily (with vitamin C to enhance absorption). Vitamin B12 500–1,000 mcg daily. Have your levels tested before starting iron supplementation.
View Top-Rated Iron + B12 on Amazon3. Vitamin D3
Vitamin D deficiency is widespread in women over 40, and one of its most reported symptoms is persistent fatigue and low mood. A study published in the North American Journal of Medical Sciences found a significant association between low vitamin D levels and fatigue, with supplementation leading to meaningful improvement [5].
Vitamin D also supports immune function, bone health, and muscle strength — all of which contribute to how energized you feel day to day. The NIH Office of Dietary Supplements notes that adults need at least 600 IU daily, though many practitioners recommend higher doses, especially for those with documented deficiency [6].
Women who spend most of their time indoors, live in northern latitudes, or have darker skin tones are at especially high risk for insufficiency.
Suggested dose: 2,000–5,000 IU daily, taken with a meal containing fat for optimal absorption. Ask your doctor to check your 25(OH)D levels.
View Top-Rated Vitamin D3 on Amazon4. Magnesium Glycinate
Magnesium is involved in over 300 enzymatic reactions in the body, including energy metabolism, muscle function, and nervous system regulation. Despite its importance, studies suggest that a significant portion of the adult population does not meet the recommended daily intake.
For energy specifically, magnesium is required for the conversion of food into ATP. Without enough magnesium, your energy production pathways simply cannot run efficiently. But magnesium also impacts energy indirectly through sleep quality. A study in the Journal of Research in Medical Sciences found that magnesium supplementation significantly improved sleep quality, sleep time, and melatonin levels [7]. Better sleep translates directly into better daytime energy.
The glycinate form of magnesium is well-absorbed and gentle on the stomach, making it ideal for daily use. Taking it in the evening supports both sleep onset and overnight recovery. For more on the sleep connection, read our in-depth article on magnesium for sleep.
Suggested dose: 200–400 mg magnesium glycinate in the evening.
View Top-Rated Magnesium on AmazonBeyond Supplements
Supplements can fill important nutritional gaps, but they work best as part of a bigger picture. Consistent, quality sleep (7–9 hours) is the single most impactful factor for sustained energy. Regular physical activity — even moderate walking — has been shown to reduce fatigue and improve mood. And chronic stress management through practices like deep breathing, yoga, or simply setting boundaries can prevent the cortisol spikes that lead to energy crashes.
Think of supplements as one pillar of your energy strategy, not the whole foundation.
Important Disclaimer: This content is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider before starting any new supplement, especially if you are pregnant, nursing, taking medications, or have an underlying health condition. Iron supplementation in particular should be guided by blood work — excess iron can be harmful.
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Editorial Standards: This article was written by Sarah Chen, a Registered Dietitian Nutritionist with over 15 years of experience in women's health. Content is reviewed quarterly for accuracy. All sources are cited inline and linked to peer-reviewed research.
Frequently Asked Questions
What is the best supplement for energy for women over 40?
CoQ10 (in the ubiquinol form) is often the most effective energy supplement for women over 40, as natural CoQ10 production declines significantly with age. However, if you have an underlying iron or B12 deficiency, addressing those first will have the biggest impact on your energy levels.
Why am I so tired at 40?
Fatigue after 40 is commonly caused by declining CoQ10 levels, hormonal changes from perimenopause, nutrient deficiencies (especially iron, B12, and vitamin D), disrupted sleep, and increased stress. Blood tests can help identify specific deficiencies, and targeted supplementation can make a significant difference.
Should I take CoQ10 in the morning or at night?
CoQ10 is best taken in the morning or early afternoon with a meal containing fat for optimal absorption. Because it supports cellular energy production, taking it later in the day may interfere with sleep for some people. Start with 100-200 mg of ubiquinol daily.
Can supplements really help with fatigue?
Yes, if your fatigue is caused by nutritional deficiencies. Studies show that iron supplementation improves fatigue even in non-anemic women with low ferritin, and CoQ10 has demonstrated anti-fatigue effects in clinical trials. However, supplements work best alongside adequate sleep, regular exercise, and stress management.
Sources
- Hernández-Camacho JD, et al. "Coenzyme Q10 Supplementation in Aging and Disease." Frontiers in Physiology. 2018;9:44. PubMed
- Mizuno K, et al. "Antifatigue effects of coenzyme Q10 during physical fatigue." Nutrition. 2008;24(4):293-299. PubMed
- NIH Office of Dietary Supplements. "Iron — Fact Sheet for Health Professionals." ods.od.nih.gov
- NIH Office of Dietary Supplements. "Vitamin B12 — Fact Sheet for Health Professionals." ods.od.nih.gov
- Roy S, et al. "Correction of Low Vitamin D Improves Fatigue: Effect of Correction of Low Vitamin D in Fatigue Study (EViDiF Study)." North American Journal of Medical Sciences. 2014;6(8):396-402. PubMed
- NIH Office of Dietary Supplements. "Vitamin D — Fact Sheet for Health Professionals." ods.od.nih.gov
- Abbasi B, et al. "The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial." Journal of Research in Medical Sciences. 2012;17(12):1161-1169. PubMed