Natural Vision Enhancers - 60 softgels | Doctor's Best
Doctor's Best Natural Vision Enhancers contain Lutemax 2020, highly bioavailable naturally sourced carotenoids that help neutralize free radicals to support healthy visual function, macular health, and cognitive acuity. Constant exposure to ultra violet (UV) and blue light emitted from computers and mobile devices may potentially damage the retina. Omega-3 DHA and EPA help support the retina's light-sensing activity.
Helps support retinal cell light-sensing capacity.
Helps protect eyes from harmful high energy blue light in everyday surroundings
Helps neutralize free radicals
- Ingredients: Cholesterol, Fish Oil Concentrate (Total Omega-3 fatty acids (as fish oil triglycerides) 285mg providing, DHA (Docosahexaenoic Acid), EPA (Eicosapentaenoic Acid)), Lutein (from Lutemax’ 2020 marigold flower ext.,(Tagetes erecta)), Zeaxanthin (from Lutemax 2020 marigold flower ext., (Tagetes erecta) OTHER INGREDIENTS: Softgel capsule (gelatin, glycerin, purified water, annatto), yellow beewax. Contains Fish (oil: Anchovy). Non-GMO, Gluten Free.
Daily Intake Amount: 2 Softgels
| Ingredient | Amount | % NRV* |
|---|---|---|
| marigold flower ext.,(Tagetes | 0 erecta) | ✝ |
| Zeaxanthin (from | 0g | ✝ |
| flower ext.,(Tagetes | 0g | ✝ |
| Lutein (from Lutemax | 0 marigold 99 | ✝ |
| EPA (Eicosapentaenoic | 45mg | ✝ |
| DHA (Docosahexaenoic | 200mg | ✝ |
| triglycerides) 285mg | 0g | ✝ |
| Total Omega-3 | 0 fish oil | ✝ |
| Fish Oil Concentrate | 500mg | ✝ |
| Cholesterol | 5mg | 1 |
| Total Fat | 1 | 1 |
| Calories | 0 eal” | ✝ |
* NRV is the Nutrient Reference Value
✝ NRV not yet established
- Directions: Take 2 softgels daily after meals, or as recommended by a nutritionally informed physician.
- Additional_Warnings: Store in a cool dry place.
Related Products
Quickview
{"id":15487064539514,"title":"Acetyl L-Carnitine, 500mg - 120 vcaps | Doctor's Best","handle":"acetyl-l-carnitine-with-biosint-carnitines-500mg-120-vcaps","description":"Science-Based Nutrition\u003cbr\u003e Helps Support Mental Focus and Alertness\u003cbr\u003e Dietary Supplement\u003cbr\u003e Vegan\u003cbr\u003e Non-GMO, Gluten Free, Soy Free\u003cbr\u003e\u003cbr\u003eAcetyl-L-Carnitine (ALC) is a naturally occurring form of L-Carnitine in the body that is involved in the metabolism of fatty acids into the universal energy molecule ATP. ALC supports the biosynthesis of acetylcholine, a key neurotransmitter for brain and nerve cell functions which regulates activities of the vital organs, blood vessels, and communication between nerves and muscles. ALC also supports levels of glutathione, a significant antioxidant sustaining neurons and protecting cellular components from superoxide radicals. \u003cbr\u003e\u003cbr\u003e Helps metabolize fatty acid to generate cellular energy \u003cbr\u003e Helps support neurotransmitter for brain and nerve cell functions \u003cbr\u003e Helps support neurons and protect cellular components from superoxide radicals","published_at":"2025-11-15T09:03:17+00:00","created_at":"2025-11-15T09:03:16+00:00","vendor":"Doctor's Best","type":"","tags":["Brand_Doctor's Best","Dieting Support","LHS","PB"],"price":2645,"price_min":2645,"price_max":2645,"available":true,"price_varies":false,"compare_at_price":null,"compare_at_price_min":0,"compare_at_price_max":0,"compare_at_price_varies":false,"variants":[{"id":56182378430842,"title":"Default Title","option1":"Default Title","option2":null,"option3":null,"sku":"P3069","requires_shipping":true,"taxable":true,"featured_image":null,"available":true,"name":"Acetyl L-Carnitine, 500mg - 120 vcaps | Doctor's Best","public_title":null,"options":["Default Title"],"price":2645,"weight":140,"compare_at_price":null,"inventory_quantity":10,"inventory_management":"shopify","inventory_policy":"deny","barcode":"753950001527","requires_selling_plan":false,"selling_plan_allocations":[],"quantity_rule":{"min":1,"max":null,"increment":1}}],"images":["\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-03-02_69a56c6b54c0c.jpg?v=1789561785"],"featured_image":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-03-02_69a56c6b54c0c.jpg?v=1789561785","options":["Title"],"media":[{"alt":"acetyl-l-carnitine,-500mg-120-vcaps","id":71752069218682,"position":1,"preview_image":{"aspect_ratio":0.999,"height":797,"width":796,"src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-03-02_69a56c6b54c0c.jpg?v=1789561785"},"aspect_ratio":0.999,"height":797,"media_type":"image","src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-03-02_69a56c6b54c0c.jpg?v=1789561785","width":796}],"requires_selling_plan":false,"selling_plan_groups":[],"content":"Science-Based Nutrition\u003cbr\u003e Helps Support Mental Focus and Alertness\u003cbr\u003e Dietary Supplement\u003cbr\u003e Vegan\u003cbr\u003e Non-GMO, Gluten Free, Soy Free\u003cbr\u003e\u003cbr\u003eAcetyl-L-Carnitine (ALC) is a naturally occurring form of L-Carnitine in the body that is involved in the metabolism of fatty acids into the universal energy molecule ATP. ALC supports the biosynthesis of acetylcholine, a key neurotransmitter for brain and nerve cell functions which regulates activities of the vital organs, blood vessels, and communication between nerves and muscles. ALC also supports levels of glutathione, a significant antioxidant sustaining neurons and protecting cellular components from superoxide radicals. \u003cbr\u003e\u003cbr\u003e Helps metabolize fatty acid to generate cellular energy \u003cbr\u003e Helps support neurotransmitter for brain and nerve cell functions \u003cbr\u003e Helps support neurons and protect cellular components from superoxide radicals"}
You may also like:
Acetyl L-Carnitine, 500mg - 120 vcaps | Doctor's Best
£26.45
Science-Based Nutrition Helps Support Mental Focus and Alertness Dietary Supplement Vegan Non-GMO, Gluten Free, Soy FreeAcetyl-L-Carnitine (ALC) is a naturally occurring form of L-Carnitine in the body that is involved...
Quickview
{"id":16205766361466,"title":"Acetyl L-Carnitine, 500mg - 60 vcaps | Doctor's Best","handle":"acetyl-l-carnitine-500mg-60-vcaps","description":"Science-Based Nutrition\u003cbr\u003e Helps Support Mental Focus and Alertness\u003cbr\u003e Dietary Supplement\u003cbr\u003e Vegan\u003cbr\u003e Non-GMO, Gluten Free, Soy Free\u003cbr\u003e\u003cbr\u003eAcetyl-L-Carnitine (ALC) is a naturally occurring form of L-Carnitine in the body that is involved in the metabolism of fatty acids into the universal energy molecule ATP. ALC supports the biosynthesis of acetylcholine, a key neurotransmitter for brain and nerve cell functions which regulates activities of the vital organs, blood vessels, and communication between nerves and muscles. ALC also supports levels of glutathione, a significant antioxidant sustaining neurons and protecting cellular components from superoxide radicals. \u003cbr\u003e\u003cbr\u003e Helps metabolize fatty acid to generate cellular energy \u003cbr\u003e Helps support neurotransmitter for brain and nerve cell functions \u003cbr\u003e Helps support neurons and protect cellular components from superoxide radicals","published_at":"2026-09-16T13:29:19+01:00","created_at":"2026-09-16T13:29:19+01:00","vendor":"Doctor's Best","type":"","tags":["PB"],"price":1525,"price_min":1525,"price_max":1525,"available":true,"price_varies":false,"compare_at_price":null,"compare_at_price_min":0,"compare_at_price_max":0,"compare_at_price_varies":false,"variants":[{"id":57274418692474,"title":"Default Title","option1":"Default Title","option2":null,"option3":null,"sku":"P30697","requires_shipping":true,"taxable":true,"featured_image":null,"available":true,"name":"Acetyl L-Carnitine, 500mg - 60 vcaps | Doctor's Best","public_title":null,"options":["Default Title"],"price":1525,"weight":0,"compare_at_price":null,"inventory_quantity":5,"inventory_management":"shopify","inventory_policy":"deny","barcode":"753950001053","requires_selling_plan":false,"selling_plan_allocations":[],"quantity_rule":{"min":1,"max":null,"increment":1}}],"images":["\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d90f556044.jpg?v=1789561765"],"featured_image":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d90f556044.jpg?v=1789561765","options":["Title"],"media":[{"alt":"acetyl-l-carnitine,-500mg-60-vcaps","id":71752066138490,"position":1,"preview_image":{"aspect_ratio":0.729,"height":597,"width":435,"src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d90f556044.jpg?v=1789561765"},"aspect_ratio":0.729,"height":597,"media_type":"image","src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d90f556044.jpg?v=1789561765","width":435}],"requires_selling_plan":false,"selling_plan_groups":[],"content":"Science-Based Nutrition\u003cbr\u003e Helps Support Mental Focus and Alertness\u003cbr\u003e Dietary Supplement\u003cbr\u003e Vegan\u003cbr\u003e Non-GMO, Gluten Free, Soy Free\u003cbr\u003e\u003cbr\u003eAcetyl-L-Carnitine (ALC) is a naturally occurring form of L-Carnitine in the body that is involved in the metabolism of fatty acids into the universal energy molecule ATP. ALC supports the biosynthesis of acetylcholine, a key neurotransmitter for brain and nerve cell functions which regulates activities of the vital organs, blood vessels, and communication between nerves and muscles. ALC also supports levels of glutathione, a significant antioxidant sustaining neurons and protecting cellular components from superoxide radicals. \u003cbr\u003e\u003cbr\u003e Helps metabolize fatty acid to generate cellular energy \u003cbr\u003e Helps support neurotransmitter for brain and nerve cell functions \u003cbr\u003e Helps support neurons and protect cellular components from superoxide radicals"}
You may also like:
Acetyl L-Carnitine, 500mg - 60 vcaps | Doctor's Best
£15.25
Science-Based Nutrition Helps Support Mental Focus and Alertness Dietary Supplement Vegan Non-GMO, Gluten Free, Soy FreeAcetyl-L-Carnitine (ALC) is a naturally occurring form of L-Carnitine in the body that is involved...
Quickview
{"id":15487064572282,"title":"Alpha-Lipoic Acid, 150mg - 120 vcaps | Doctor's Best","handle":"alpha-lipoic-acid-150mg-120-vcaps","description":"\u003cp\u003eScience-Based Nutrition\u003cbr\u003eDietary Supplement\u003cbr\u003eHelps Support Glucose Metabolism and Regenerate Antioxidants\u003cbr\u003eNon-GMO \/ Gluten Free \/ Soy Free\u003cbr\u003eVegan\u003cbr\u003e\u003cbr\u003eAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy in the body. ALA is naturally occurring and functions as an antioxidant throughout the body that helps regenerate other antioxidants such as vitamin C, vitamin E and glutathione. ALA is a distinct antioxidant that is both hydrophobic and hydrophilic, optimizing support to the body's capability in buffering free radicals for overall well-being.\u003c\/p\u003e\n\u003cp\u003eHelps support glucose metabolism for cellular energy\u003cbr\u003eHelps regenerate antioxidants such as vitamin C, vitamin E and glutathione\u003cbr\u003eHelps support the body to buffer free radicals\u003c\/p\u003e","published_at":"2025-11-15T09:03:19+00:00","created_at":"2025-11-15T09:03:18+00:00","vendor":"Doctor's Best","type":"","tags":["Brand_Doctor's Best","HMMCT","LHS","PB"],"price":1600,"price_min":1600,"price_max":1600,"available":true,"price_varies":false,"compare_at_price":null,"compare_at_price_min":0,"compare_at_price_max":0,"compare_at_price_varies":false,"variants":[{"id":56182378463610,"title":"Default Title","option1":"Default Title","option2":null,"option3":null,"sku":"P6155","requires_shipping":true,"taxable":true,"featured_image":null,"available":true,"name":"Alpha-Lipoic Acid, 150mg - 120 vcaps | Doctor's Best","public_title":null,"options":["Default Title"],"price":1600,"weight":110,"compare_at_price":null,"inventory_quantity":9,"inventory_management":"shopify","inventory_policy":"deny","barcode":"753950001046","requires_selling_plan":false,"selling_plan_allocations":[],"quantity_rule":{"min":1,"max":null,"increment":1}}],"images":["\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a1991fe6f47.jpg?v=1789561773"],"featured_image":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a1991fe6f47.jpg?v=1789561773","options":["Title"],"media":[{"alt":"alpha-lipoic-acid,-150mg-120-vcaps","id":71752067318138,"position":1,"preview_image":{"aspect_ratio":1.0,"height":597,"width":597,"src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a1991fe6f47.jpg?v=1789561773"},"aspect_ratio":1.0,"height":597,"media_type":"image","src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a1991fe6f47.jpg?v=1789561773","width":597}],"requires_selling_plan":false,"selling_plan_groups":[],"content":"\u003cp\u003eScience-Based Nutrition\u003cbr\u003eDietary Supplement\u003cbr\u003eHelps Support Glucose Metabolism and Regenerate Antioxidants\u003cbr\u003eNon-GMO \/ Gluten Free \/ Soy Free\u003cbr\u003eVegan\u003cbr\u003e\u003cbr\u003eAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy in the body. ALA is naturally occurring and functions as an antioxidant throughout the body that helps regenerate other antioxidants such as vitamin C, vitamin E and glutathione. ALA is a distinct antioxidant that is both hydrophobic and hydrophilic, optimizing support to the body's capability in buffering free radicals for overall well-being.\u003c\/p\u003e\n\u003cp\u003eHelps support glucose metabolism for cellular energy\u003cbr\u003eHelps regenerate antioxidants such as vitamin C, vitamin E and glutathione\u003cbr\u003eHelps support the body to buffer free radicals\u003c\/p\u003e"}
You may also like:
Alpha-Lipoic Acid, 150mg - 120 vcaps | Doctor's Best
£16.00
Science-Based NutritionDietary SupplementHelps Support Glucose Metabolism and Regenerate AntioxidantsNon-GMO / Gluten Free / Soy FreeVeganAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy...
Quickview
{"id":16205766754682,"title":"Alpha-Lipoic Acid, 600mg - 180 vcaps | Doctor's Best","handle":"alpha-lipoic-acid-600mg-180-vcaps","description":"\u003cp\u003eScience-Based Nutrition\u003cbr\u003eDietary Supplement\u003cbr\u003eHelps Support Glucose Metabolism and Regenerate Antioxidants\u003cbr\u003eNon-GMO \/ Gluten Free \/ Soy Free\u003cbr\u003eVegan\u003cbr\u003e\u003cbr\u003eAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy in the body. ALA is naturally occurring and functions as an antioxidant throughout the body that helps regenerate other antioxidants such as vitamin C, vitamin E and glutathione. ALA is a distinct antioxidant that is both hydrophobic and hydrophilic, optimizing support to the body's capability in buffering free radicals for overall well-being.\u003c\/p\u003e\n\u003cp\u003eHelps support glucose metabolism for cellular energy\u003cbr\u003eHelps regenerate antioxidants such as vitamin C, vitamin E and glutathione\u003cbr\u003eHelps support the body to buffer free radicals\u003c\/p\u003e","published_at":"2026-09-16T13:29:43+01:00","created_at":"2026-09-16T13:29:42+01:00","vendor":"Doctor's Best","type":"","tags":["HMMCT","PB"],"price":4475,"price_min":4475,"price_max":4475,"available":true,"price_varies":false,"compare_at_price":null,"compare_at_price_min":0,"compare_at_price_max":0,"compare_at_price_varies":false,"variants":[{"id":57274419282298,"title":"Default Title","option1":"Default Title","option2":null,"option3":null,"sku":"P32807","requires_shipping":true,"taxable":true,"featured_image":null,"available":true,"name":"Alpha-Lipoic Acid, 600mg - 180 vcaps | Doctor's Best","public_title":null,"options":["Default Title"],"price":4475,"weight":0,"compare_at_price":null,"inventory_quantity":10,"inventory_management":"shopify","inventory_policy":"deny","barcode":"753950002494","requires_selling_plan":false,"selling_plan_allocations":[],"quantity_rule":{"min":1,"max":null,"increment":1}}],"images":["\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d95590df0b.jpg?v=1789561789"],"featured_image":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d95590df0b.jpg?v=1789561789","options":["Title"],"media":[{"alt":"alpha-lipoic-acid,-600mg-180-vcaps","id":71752069349754,"position":1,"preview_image":{"aspect_ratio":0.749,"height":597,"width":447,"src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d95590df0b.jpg?v=1789561789"},"aspect_ratio":0.749,"height":597,"media_type":"image","src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-24_699d95590df0b.jpg?v=1789561789","width":447}],"requires_selling_plan":false,"selling_plan_groups":[],"content":"\u003cp\u003eScience-Based Nutrition\u003cbr\u003eDietary Supplement\u003cbr\u003eHelps Support Glucose Metabolism and Regenerate Antioxidants\u003cbr\u003eNon-GMO \/ Gluten Free \/ Soy Free\u003cbr\u003eVegan\u003cbr\u003e\u003cbr\u003eAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy in the body. ALA is naturally occurring and functions as an antioxidant throughout the body that helps regenerate other antioxidants such as vitamin C, vitamin E and glutathione. ALA is a distinct antioxidant that is both hydrophobic and hydrophilic, optimizing support to the body's capability in buffering free radicals for overall well-being.\u003c\/p\u003e\n\u003cp\u003eHelps support glucose metabolism for cellular energy\u003cbr\u003eHelps regenerate antioxidants such as vitamin C, vitamin E and glutathione\u003cbr\u003eHelps support the body to buffer free radicals\u003c\/p\u003e"}
You may also like:
Alpha-Lipoic Acid, 600mg - 180 vcaps | Doctor's Best
£44.75
Science-Based NutritionDietary SupplementHelps Support Glucose Metabolism and Regenerate AntioxidantsNon-GMO / Gluten Free / Soy FreeVeganAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy...
Quickview
{"id":16205766689146,"title":"Alpha-Lipoic Acid, 600mg - 60 vcaps | Doctor's Best","handle":"alpha-lipoic-acid-600mg-60-vcaps","description":"\u003cp\u003eScience-Based Nutrition\u003cbr\u003eDietary Supplement\u003cbr\u003eHelps Support Glucose Metabolism and Regenerate Antioxidants\u003cbr\u003eNon-GMO \/ Gluten Free \/ Soy Free\u003cbr\u003eVegan\u003cbr\u003e\u003cbr\u003eAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy in the body. ALA is naturally occurring and functions as an antioxidant throughout the body that helps regenerate other antioxidants such as vitamin C, vitamin E and glutathione. ALA is a distinct antioxidant that is both hydrophobic and hydrophilic, optimizing support to the body's capability in buffering free radicals for overall well-being.\u003c\/p\u003e\n\u003cp\u003eHelps support glucose metabolism for cellular energy\u003cbr\u003eHelps regenerate antioxidants such as vitamin C, vitamin E and glutathione\u003cbr\u003eHelps support the body to buffer free radicals\u003c\/p\u003e","published_at":"2026-09-16T13:29:43+01:00","created_at":"2026-09-16T13:29:42+01:00","vendor":"Doctor's Best","type":"","tags":["HMMCT","PB"],"price":1945,"price_min":1945,"price_max":1945,"available":true,"price_varies":false,"compare_at_price":null,"compare_at_price_min":0,"compare_at_price_max":0,"compare_at_price_varies":false,"variants":[{"id":57274419216762,"title":"Default Title","option1":"Default Title","option2":null,"option3":null,"sku":"P3070","requires_shipping":true,"taxable":true,"featured_image":null,"available":true,"name":"Alpha-Lipoic Acid, 600mg - 60 vcaps | Doctor's Best","public_title":null,"options":["Default Title"],"price":1945,"weight":0,"compare_at_price":null,"inventory_quantity":10,"inventory_management":"shopify","inventory_policy":"deny","barcode":"753950001336","requires_selling_plan":false,"selling_plan_allocations":[],"quantity_rule":{"min":1,"max":null,"increment":1}}],"images":["\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a19a211b93a.jpg?v=1789561788"],"featured_image":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a19a211b93a.jpg?v=1789561788","options":["Title"],"media":[{"alt":"alpha-lipoic-acid,-600mg-60-vcaps","id":71752069316986,"position":1,"preview_image":{"aspect_ratio":0.998,"height":597,"width":596,"src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a19a211b93a.jpg?v=1789561788"},"aspect_ratio":0.998,"height":597,"media_type":"image","src":"\/\/lifestylevitamins.co.uk\/cdn\/shop\/files\/image_2026-02-27_69a19a211b93a.jpg?v=1789561788","width":596}],"requires_selling_plan":false,"selling_plan_groups":[],"content":"\u003cp\u003eScience-Based Nutrition\u003cbr\u003eDietary Supplement\u003cbr\u003eHelps Support Glucose Metabolism and Regenerate Antioxidants\u003cbr\u003eNon-GMO \/ Gluten Free \/ Soy Free\u003cbr\u003eVegan\u003cbr\u003e\u003cbr\u003eAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy in the body. ALA is naturally occurring and functions as an antioxidant throughout the body that helps regenerate other antioxidants such as vitamin C, vitamin E and glutathione. ALA is a distinct antioxidant that is both hydrophobic and hydrophilic, optimizing support to the body's capability in buffering free radicals for overall well-being.\u003c\/p\u003e\n\u003cp\u003eHelps support glucose metabolism for cellular energy\u003cbr\u003eHelps regenerate antioxidants such as vitamin C, vitamin E and glutathione\u003cbr\u003eHelps support the body to buffer free radicals\u003c\/p\u003e"}
You may also like:
Alpha-Lipoic Acid, 600mg - 60 vcaps | Doctor's Best
£19.45
Science-Based NutritionDietary SupplementHelps Support Glucose Metabolism and Regenerate AntioxidantsNon-GMO / Gluten Free / Soy FreeVeganAlpha-lipoic acid (ALA) plays an important role in the metabolism of glucose that produces cellular energy...